Keeping a healthy blood pressure is an essential part of staying healthy. After all, high blood pressure can cause heart disease, strokes, kidney disease, and more.

But what about low blood pressure? Low blood pressure can be just as dangerous as high blood pressure - sometimes, even more so.

While high blood pressure can lead to health problems over time, low blood pressure can be a threat in the short term. When your blood pressure is low, also called hypotension, it becomes harder for blood to reach vital organs, including your brain. When your brain doesn't get enough blood, you can pass out. Other organs can be damaged from not getting enough blood, too.

So, how do you know if your blood pressure is low? What kinds of conditions cause low blood pressure? And when your blood pressure is low, what can you do to fix it?

What is low blood pressure?

You can think of blood pressure in your body in the same way you think about water pressure in your house. If your water pressure is too low, the flow of water to your faucets is affected. The same is true for blood in your body. When blood pressure is too low, the flow of blood to your vital organs (most importantly, the brain) is affected.

A normal blood pressure is one that is below:

• 120 mmHg systolic (the top number)

• 80 mmHg diastolic (the bottom number)

Technically, blood pressure is considered low when it drops below:

• 90 mmHg systolic (the top number)

• 60 mmHg diastolic (the bottom number)

Your baseline blood pressure matters just as much as the numbers

But it's not just about the numbers. It also matters what your usual blood pressure is and whether you're experiencing symptoms.

For instance, some people always have a blood pressure that runs low, and it feels normal for them. If your blood pressure always runs low, your reading isn't very different from usual, and you don't have any symptoms, that may be OK for you.

On the other hand, if your blood pressure drops from what's considered a normal level, and you have symptoms, then that's more concerning.

And, it's also cause for worry if your blood pressure usually runs high, but you have a drop to what's considered a normal blood pressure level, and you have symptoms.

What are low blood pressure symptoms?

Most symptoms of low blood pressure are symptoms of low blood flow to the brain.

But you may feel other symptoms related to your heart. This is because when blood pressure drops, your heart works overboard to try to keep blood pressure up. Increasing your heart rate is a short-term fix to keep blood flowing to the brain and other major organs.

These are some common symptoms of low blood pressure you may experience:

• Lightheadedness

• Dizziness

• Feeling faint

• Blurred vision

More serious symptoms of low blood pressure include:

• Racing heart or palpitations

• Weakness

• Unsteadiness

• Confusion

• Nausea or vomiting

• Headache

• Passing small amounts of dark urine

• Fainting (syncope)

You may experience other symptoms, too, depending on the underlying cause for your low blood pressure. But these are not specific to low blood pressure. For example, you may have chest pain or shortness of breath, a fever, a rash, abdominal pain, vomiting or diarrhea, and difficulty passing urine.

Why you should always pay attention to low blood pressure symptoms

Most people can handle a little variation in their blood pressure. In fact, the body has developed ways to preserve blood flow to the organs - and especially the brain - at all costs.

So if your blood pressure is low and stays low, and you start to experience symptoms, that's a sign the body is running out of options and starting to struggle. It's also a sign you need urgent medical care.

Common causes of low blood pressure

Anyone who's had their blood pressure checked at the doctor's office knows that the numbers are always changing. That's because blood pressure is affected by lots of things, like your position, your activity level, and whether you drank a cup of coffee this morning. Your blood pressure can even change if you're feeling stressed.

In other words, it's completely normal for your blood pressure to go up or down throughout the day for a variety of reasons. And, our bodies are designed to deal with these daily ups and downs in blood pressure.

But sometimes, blood pressure can get too low, and it can become a problem. The body can no longer compensate for the low blood pressure, and things start to fall apart.

Here are eight common reasons why low blood pressure can happen.

1. Dehydration

Your blood is mostly made of water. So when you're dehydrated, the volume of blood in your blood vessels goes down. In severe cases, this can cause your blood pressure to drop.

Low blood pressure from severe dehydration most commonly happens as a result of heavy diarrhea or vomiting, especially in young children, people with serious medical conditions, and people older than 70 years. But, anyone can be affected. This is why it's important to stay hydrated when you're not feeling well.

2. Vasovagal reaction

The vagus nerve is a long and important nerve. It connects the brain to the heart and your abdominal organs. It has a generally calming effect and is a key player in the "freeze" part of the fight-flight-freeze response.

When the vagus nerve is activated, the heart rate slows and blood pressure drops. This is known as a vasovagal reaction. Your vagus nerve can be activated by things like emotional stress, the sight of blood, pain, vomit, or even just standing upright for too long.

When a vasovagal reaction is severe, it can cause you to black out, a condition also known as vasovagal syncope. This is the medical term for fainting or passing out.

3. Orthostatic hypotension

If you've ever felt lightheaded after standing up too quickly, you've probably experienced orthostatic hypotension. Orthostatic hypotension happens when you change position from sitting to standing, but your body is a little delayed in responding to your new position. As a result, gravity momentarily causes your blood to pool to your legs, and your blood pressure can drop.

Orthostatic hypotension is usually temporary and gets better after a few seconds. And other factors can worsen this reaction like some medications, dehydration, and older age. If you're someone who experiences this a lot, it can help to take your time standing up from a lying or seated position.

4. Postprandial hypotension

When you eat, your digestive system needs an extra boost of blood flow. In some people, this extra blood being routed to your digestive tract causes too little blood flow in other areas, including the brain. This results in something known as postprandial hypotension, a fancy term for having low blood pressure after a meal.

5. Heart problems

Your heart is the pump that creates blood pressure within your body. So when your heart isn't working well, it's less able to maintain good blood pressure. Some types of heart problems that lead to low blood pressure are heart failure, abnormal heart rhythms, and heart attacks.

6. Prescription medications

Lots of different medications list low blood pressure as a side effect. Some medicines that cause your blood pressure to drop include:

• Opioid pain medications

• Antidepressants (specifically tricyclic antidepressants and monoamine oxidase inhibitors)

• Anxiety medications (benzodiazepines)

• Diuretics (also known as water pills)

• Heart rhythm medications (beta blockers, calcium channel blockers)

• Erectile dysfunction medications

If you experience symptoms of low blood pressure soon after starting a new medication, let your medical team know. Your doctor (or other prescriber) can adjust the dose or work with you to transition on to a different medication that suits you better.

7. Pregnancy

The physical and hormonal changes of pregnancy can cause your blood pressure to drop. This is usually most noticeable during the first and second trimesters. By the third trimester, blood pressure should return to baseline.

Low blood pressure during pregnancy is usually normal and safe for the baby. Most times, you don't feel any symptoms as a result. However, if you feel symptoms of low blood pressure, get it checked out right away. Having consistently low blood pressure could mean your baby isn't getting enough blood.

8. Autonomic dysfunction

The autonomic nervous system controls functions like your heart rate, blood pressure, and breathing. When the autonomic nervous system doesn't function as it's meant to, your blood pressure can increase or decrease abnormally.

Autonomic dysfunction is what happens in two conditions on this list: vasovagal syncope and orthostatic hypotension.

But many conditions can lead to autonomic dysfunction. Some examples include:

• Parkinson's disease (PD)

• Amyloidosis

• Rheumatoid arthritis

• Lupus

• Postural tachycardia syndrome (PoTS)

• Diabetes

• Lyme disease

Severe causes of low blood pressure that require emergency care

Sometimes, low blood pressure can be a sign of a medical emergency. In medicine, it's called being "in shock."

The word "shock" in medical language means something different than in everyday speech. In medicine, it specifically means that your circulatory system has failed to meet the demands of your body. In other words, the amount of blood and blood pressure in your blood vessels has become dangerously low.

Shock can be caused by a number of different things. No matter the cause, it's always a life-threatening emergency that requires urgent medical care.

Some causes of shock include:

• Severe infection (known as septic shock)

• A severe allergic reaction (known as anaphylactic shock)

• A serious heart problem (known as cardiogenic shock)

• Severe loss of blood or severe anemia (known as hypovolemic shock)

When should you get medical care for low blood pressure symptoms?

One low blood pressure reading is usually not cause for concern. If you have one low blood pressure measurement but you feel OK, there are a few things you can do at home to see if your blood pressure improves.

Try the following, and then get a few repeat blood pressure readings, a few minutes apart:

• Sit or lie down quietly for 5 minutes.

• Raise your legs above the level of your heart.

• Make sure your arm is at the level of your heart (not too high, not too low).

• Check that your cuff is connected properly to the blood pressure machine and is inflating well.

Get nonurgent medical help

In some cases, it may be OK to wait it out, or call your primary care provider during business hours. For example:

• You have low blood pressure, but you usually run low, and you feel OK.

• You had low blood pressure, but it's come back up to normal.

Emergency medical help

There are some situations where you shouldn't try to figure things out on your own at home. Because low blood pressure can get serious fast, it's best not to take any chances. Especially if you're experiencing symptoms.

You should always call 911 or go to the ER (not urgent care) if:

• You have persistently low blood pressure, but you usually run normal or high.

• You have persistently low blood pressure that isn't improving.

Likewise, if you have low blood pressure and any of the following symptoms, you should also call 911 or go to the ER:

• You have a high (or low) heart rate.

• You have any type of infection, like a chest infection, urine infection, or skin infection.

• You have severe abdominal pain, or blood in your stool.

• You experience vomiting, or diarrhea, and can't keep food or drink down.

• You've had an allergic reaction.

• You have heart failure.