Your vision may dim or blur or you could have tunnel vision. To add to this already frightening experience, you may also feel confusion and dizziness. Less commonly, you could have dull pain across the back of your neck and shoulders. Rarely, you could lose consciousness or faint. These are symptoms of a condition called orthostatic hypotension, which results when blood pressure drops excessively due to a change in position. Who can have orthostatic hypotension? It is very common, especially among older people, affecting approximately 18 percent of those over 65, notes a 2011 review in American Family Physician. It becomes even more prevalent as people age, with up to half of elderly people living in institutions, such as nursing homes, meeting the definition for orthostatic hypotension, according to a 2013 position paper in Journal of Clinical Hypertension. Does orthostatic hypotension go away? Typically, yes, an episode of hypotension ends quickly; once you sit or lie down, symptoms disappear. The biggest risk for most people who have orthostatic hypotension is injury from a fall. But if you have chronic or recurrent orthostatic hypotension, it may indicate a more serious underlying condition. Here are 10 essential facts about orthostatic hypotension:

1. Most Episodes of Orthostatic Hypotension Go Unnoticed

How does your doctor check for orthostatic hypotension? The technical definition is that you have a 20-point drop in the systolic, or higher, number of a blood pressure reading, or a 10-point fall in the lower, or diastolic, number, within three minutes of standing. But your blood pressure can drop without resulting in any symptoms at all. “While the blood pressure criteria for a diagnosis of orthostatic hypotension are frequently met in clinical practice, only a small portion of patients with this condition complains of symptoms,” says Umberto Campia, MD, director of vascular medicine at MedStar Heart & Vascular Institute in Washington, D.C.

2. Gravity Is the Basic Culprit

What causes orthostatic hypotension? When you’re lying down, your blood is evenly distributed throughout your body. When you stand up, gravity causes blood to pool in your legs. “Normally, blood vessels in the lower body constrict when we stand up — also known as vasoconstriction — to prevent the blood pressure from dropping too much as we change position,” explains Guy Mayeda, MD, a cardiologist at Good Samaritan Hospital in Los Angeles. If this compensation fails to occur rapidly enough or strongly enough, blood flow to your brain can decrease and become briefly starved of oxygen. The brain is extremely sensitive to low oxygen levels, and that leads to dizziness and other symptoms.

3. Orthostatic Hypotension Usually Resolves Quickly

Most episodes of dizziness from orthostatic hypotension last only seconds. In the vast majority cases, the cardiovascular system belatedly adjusts, adequate blood flow to the brain resumes, and symptoms disappear. If you’re experiencing orthostatic hypotension symptoms and you sit or lie back down, relief should be almost instantaneous as gravity’s interference lessens. The emotional aftermath, however, can have a significant and lasting effect. “It is something that can be quite scary and concerning, especially if you pass out,” says Martha Gulati, MD, associate professor of cardiovascular medicine at the Ohio State University Wexner Medical Center in Columbus.

4. Age Is One of the Biggest Risk Factors for Orthostatic Hypotension

As people age, the cardiovascular reflexes responsible for vasoconstriction with standing become less able to react quickly. Also, aging brains are more susceptible to the effects of lower blood pressure. “The older someone is, the more sensitive they are to the lack of blood flow and oxygen to the brain,” says Diana Heiman, MD, associate professor of family medicine at East Tennessee State University in Johnson City, Tennessee. “Younger people can accommodate better. They have more of a reserve of working neurons.” At any age, orthostatic hypotension may result from sitting too long in a hot tub or even hot sun, or from prolonged sitting, such as on a plane. “Other common causes can be the use of medications, particularly diuretics or high blood pressure medicines,” says Laura Martin, MD, associate professor of clinical family and community medicine at Temple University School of Medicine in Philadelphia.

5. Dehydration Is One of the Most Common Causes

Can dehydration cause orthostatic hypotension? Yes, dehydration can reduce the volume of blood circulating through your vessels, which can cause a drop in blood pressure, along with increased susceptibility to orthostatic hypotension. Low blood volume can be caused by vomiting, diarrhea, and bleeding. But the most likely culprit is outdoor activity in hot weather, which can exacerbate fluid loss from perspiration. Unless you replace fluid by drinking water or other liquids, you may be at risk for orthostatic hypotension. “It’s to be expected if you’re been out in the heat, or you’re anemic, or you’ve been vomiting,” says Caitlin Giesler, MD, internist and specialist in cardiovascular diseases at Seton Heart Institute in Austin, Texas.

6. Orthostatic Hypotension Particularly Affects Healthy Exercisers

Exercise is a protective factor for many health conditions, but orthostatic hypotension is particularly common among endurance athletes and other healthy, fit people. Although marathon runners may already have resting heart rates as low as 40 beats per minute, considerably less than the 60 to 100 beats per minute considered normal — this is less likely a cause of dizziness. Instead, it might be related to fluid loss, as exercise can lead to dehydration. This type of orthostatic hypotension is generally harmless.

7. You Should See Your Doctor if You Have an Episode

Although orthostatic hypotension is rarely harmful, consider making a doctor’s appointment if you experience it for the first time. “It should be taken seriously because studies have shown that people with orthostatic hypotension are at higher risk of developing cardiovascular problems in the future,” says Kristine Arthur, MD, an internist at Orange Coast Memorial Medical Center in Fountain Valley, California. There is a link between orthostatic hypotension and increased risk of congestive heart failure, Arthur adds. Orthostatic hypotension could also be a sign of other aliments, including diabetic neuropathy, thyroid problems, and Parkinson’s disease.

8. Diagnosis Is Quick, Simple, and Painless

How do you measure orthostatic hypotension? The usual method for diagnosis is to have the person lie on a tilt table while a blood pressure reading is taken. The table is tilted so the patient is vertical and blood pressure is taken again. If the change in readings falls within the defined range, the person has orthostatic hypotension. Diagnosing the cause of the low blood pressure may be more complex and involve assessing medications and doing an ultrasound of the heart. You can get the most out of your visit for a hypotension episode by coming in with details to share:

When the problem occurredWhat you were doing before it happenedHow long it lastedWhether you felt anything other than dizziness, such as shortness of breath, pain, or heart palpitations

9. A Variety of Treatments Work for Orthostatic Hypotension

If your hypotension episodes are more than occasional and brief, your doctor may decide to treat them. Most treatments involve modifying behavior, such as increasing your liquid intake to reduce dehydration. If you are taking blood pressure medicines, your doctor may change your dosage or medication. Less commonly, your doctor may ask you to increase your sodium intake, or prescribe medications designed to increase your blood pressure. Often, testing reveals no specific cause, so different approaches are applied until something works.

10. Behavior Modification Is Often the Best Treatment

How can you prevent orthostatic hypotension? Simply pausing for a minute before rising from bed can significantly reduce episodes of orthostatic hypotension, because this allows your cardiovascular system to adjust. This is especially relevant when you’ve been sleeping and are getting up in the middle of the night. Here are other ways to reduce the number or risks of orthostatic hypotension episodes:

Keep one hand on a rail or support when rising.Be ready to sit or lie back down quickly if symptoms begin.Stay hydrated.Take medications at bedtime.

Your doctor may also recommend wearing compression socks to reduce blood pooling in your legs.