Why do I feel lightheaded when I stand up quickly?

Many people have experienced the so-called 'lightheadedness', which is when you lose your sense of balance and feel as if your eyes suddenly become dark just after getting up from a chair. The science news site Live Science explains what mechanism causes this lightheadedness.

Why do you get dizzy if you stand up too fast? | Live Science
https://www.livescience.com/health/heart-circulation/why-do-you-get-dizzy-if-you-stand-up-too-fast

Lightheadedness is called orthostatic hypotension or postural hypotension and is caused by a sudden change in body position. Sudden changes in body position, such as suddenly standing up from a sitting position, result in the brain not getting enough blood and oxygen, and at the same time, the light-sensing retina receives less oxygen. A lack of oxygen in the retina leads to temporary vision loss.

When you suddenly stand up, approximately 300 to 800 ml of blood is pulled into your lower body, causing a temporary drop in blood pressure. A sudden drop in blood pressure is detected by pressure-sensitive nerve receptors, causing blood vessels to constrict, muscles in the lower body to contract, and heart rate to increase. These systems that stabilize blood pressure are controlled by the autonomic nervous system , which regulates involuntary bodily functions such as heart rate, breathing, and digestion, and usually do not have a major impact on health.

However, if you are dehydrated or have a serious illness, your blood pressure will drop more significantly and take longer to stabilize. Also, if you are taking some antihypertensive drugs, you may be more likely to experience dizziness due to a drop in blood pressure. Some people also find that their blood pressure drops right after they wake up in the morning, so they tend to feel lightheaded when they get out of bed.

The National Institute of Neurological Disorders and Stroke in the United States classifies orthostatic hypotension into two types: primary and secondary. Primary causes are damage to the autonomic nervous system due to nerve damage, etc. Secondary cases are caused by slow heart rate, low blood sugar, thyroid conditions, etc., and secondary cases are relatively more common than primary cases.

Aging is also one of the causes of orthostatic hypotension. As we age, blood pressure sensors in the neck and heart become less responsive, making it difficult for the heart to regulate itself. Therefore, people over the age of 65 are more likely to experience lightheadedness.

In addition, if you experience lightheadedness frequently or continue for a long time, your health condition may be deteriorating, says Steven Jerashek, an associate professor at Harvard Medical School. It is pointed out that if it lasts for more than 3 minutes after standing up, it is a problem.