Orthostasis is the body’s physiological challenge of maintaining blood pressure when you stand up. The term comes from the Greek for “standing upright,” and it refers to the stress that gravity places on your cardiovascular system every time you shift from lying down or sitting to a standing position. When this system works well, you don’t notice it. When it doesn’t, the result is orthostatic hypotension: a drop in blood pressure that causes dizziness, lightheadedness, or even fainting.
What Happens in Your Body When You Stand
The moment you stand, gravity pulls roughly 500 to 800 milliliters of blood downward into your legs and abdomen. This sudden shift reduces the amount of blood returning to your heart, which briefly lowers blood pressure. In a healthy person, the body corrects this within seconds through a reflex loop controlled by pressure sensors called baroreceptors, located in your neck and chest.
These sensors detect the drop in pressure and signal your nervous system to respond. Your heart rate increases, your blood vessels tighten, and nerve activity ramps up to push blood back toward your brain and vital organs. During standing, the nervous system actually becomes more sensitive to rapid pressure changes, amplifying its response to compensate for the reduced efficiency of blood vessel constriction in the lower body. It also resets its baseline to maintain a higher level of nerve signaling overall. This entire process happens automatically, without any conscious effort.
When the Reflex Fails
Orthostatic hypotension is diagnosed when standing causes a blood pressure drop of 20 mmHg or more in the upper number (systolic), or 10 mmHg or more in the lower number (diastolic). The most common symptoms are lightheadedness and dizziness upon standing, and they typically last less than a few minutes. Other signs include blurry vision, weakness, confusion, and in more severe cases, fainting.
This is not a rare problem. Among adults 65 and older, roughly 28% of the general population and 35% of those visiting geriatric clinics experience it. The numbers are likely even higher than what’s traditionally been reported, because continuous blood pressure monitoring catches brief drops that standard office measurements miss.
Common Causes and Risk Factors
Dehydration is one of the most straightforward causes. When your blood volume is low from not drinking enough fluids, sweating heavily, or illness, there’s simply less blood available to circulate when you stand. Prolonged bed rest weakens the body’s ability to compensate for posture changes, which is why orthostasis is common after surgery or hospitalization.
Several medical conditions impair the autonomic nervous system, which controls the standing reflex. Parkinson’s disease, diabetes (which can damage the nerves that regulate blood vessels), and alcoholism are among the most common. Postural orthostatic tachycardia syndrome (POTS) is a related condition where the heart rate increases excessively upon standing, often causing similar symptoms even without a dramatic blood pressure drop.
Medications That Increase Risk
Certain drug classes significantly raise the odds of orthostatic hypotension. A large meta-analysis of randomized trials found that beta-blockers carried the highest risk, increasing the odds nearly eightfold compared to placebo. Older tricyclic antidepressants were close behind, with about a sixfold increase. Alpha-blockers (commonly prescribed for prostate symptoms), antipsychotics, centrally acting blood pressure medications, and a class of diabetes drugs called SGLT-2 inhibitors all roughly doubled the odds.
Interestingly, some blood pressure medications you might expect to be culprits, like ACE inhibitors, calcium channel blockers, and SSRIs, showed no statistically significant increase in orthostatic hypotension compared to placebo. If you’re taking a tricyclic antidepressant and experiencing dizziness on standing, this is worth discussing with your prescriber, since SSRIs are generally preferred partly because of this lower risk.
How It’s Diagnosed
The simplest test is a blood pressure check in two positions. Your blood pressure is measured while you’re lying down, then again after you’ve been standing for one to three minutes. A qualifying drop, combined with symptoms, confirms the diagnosis.
For more complex or unclear cases, a tilt table test provides a controlled evaluation. You lie flat on a table with straps holding you in place while your heart rate and blood pressure are monitored. After about five minutes, the table tilts upward to simulate standing. You stay in this position for anywhere from 5 to 45 minutes. If no symptoms appear, a medication may be given through an IV to provoke the nervous system response. A positive result means your blood pressure drops and symptoms develop during the tilt. A negative result means your blood pressure stays stable and you feel fine throughout.
Managing Orthostasis Day to Day
The first line of management is increasing blood volume through fluids and salt. Guidelines recommend drinking five to eight 8-ounce glasses of water or other fluids per day (about 1.25 to 2.5 liters), and increasing sodium intake to 10 to 20 grams of salt daily. If adding salt to food isn’t appealing, salty soups, pretzels, potato chips, or salt tablets (typically 2 grams taken three times a day) can fill the gap. At minimum, aim for at least one glass of fluid with every meal and at least two glasses at other times throughout the day.
Simple habits also make a difference. Standing up slowly, especially first thing in the morning, gives the reflex time to activate. Sleeping with the head of your bed slightly elevated can reduce the severity of the blood pressure drop when you get up. Avoiding prolonged standing in hot environments helps, since heat dilates blood vessels and worsens pooling.
Physical Countermaneuvers
Specific body movements can raise blood pressure quickly by squeezing blood out of your leg and abdominal muscles and back toward your heart. These are especially useful when you feel symptoms coming on. The most effective options, supported by research across multiple populations, include crossing your legs while tensing your thigh muscles, squatting, and tensing your arms or upper body. Squatting produces some of the largest and most consistent blood pressure increases across studies. Leg crossing combined with muscle tensing has been shown to raise both systolic and diastolic pressure meaningfully in people with orthostatic hypotension.
Even smaller movements help. Fidgeting your legs while standing, doing calf raises, or shifting your weight from foot to foot all promote blood flow back to the heart. Some people find that combining movements works best. For example, rising slowly from a squat while tensing the legs can prevent the brief dip in pressure that sometimes occurs when transitioning to full standing. These maneuvers are also recommended for people prone to fainting during blood draws or vaccinations.
Who’s Most Affected
Age is the single biggest risk factor. The baroreceptor reflex becomes less responsive with age, blood vessels stiffen, and older adults are more likely to take medications that compound the problem. People with neurological conditions like Parkinson’s disease or multiple system atrophy often develop severe, persistent orthostatic hypotension because the nerve pathways controlling blood vessel tone deteriorate. Astronauts returning from space experience pronounced orthostasis because prolonged weightlessness deconditions the cardiovascular system in much the same way that extended bed rest does.
For younger adults, orthostasis most commonly results from dehydration, medication side effects, or conditions like POTS. In these cases, increasing fluid and salt intake, adjusting medications, and using physical countermaneuvers often provide substantial relief.