For some people, older ones in particular, blood pressure drops excessively when they stand up; it is a condition called postural or orthostatic hypotension. Symptoms of dizziness, blurred vision, confusion or faintness occur when standing up, especially after lying or sitting for a long time. Some people may fall, faint or have a brief seizure.
Similar symptoms are experienced by some younger people upon standing up; their heart rate increases more than normal but without a drop in blood pressure. This condition is called POTS (postural orthostatic tachycardia syndrome); it is not yet clear why such people feel dizzy despite having no drop in blood pressure.
When people stand, gravity causes blood to pool in the veins of the legs, and this pooling lowers the amount of blood the heart pumps to the brain. Dizziness is caused by the low blood flow to the brain together with other symptoms.
The nervous system, as compensation, quickly constricts blood vessels and increases the heart rate, so that blood pressure returns to normal before symptoms develop; the automatic nervous system is the responsible part for this compensation.
The common causes for new dizziness upon standing up include drugs, decreased blood volume due to blood loss or dehydration, prolonged bed rest and adrenal insufficiency. The common causes for chronic dizziness upon standing include malfunction of automatic nervous system and age- related changes in blood pressure regulation.
Some causes can be cured and some cannot be, and people must take measures including lifestyle changes and drugs to decrease their symptoms. People who are sitting or lying down should rise carefully and slowly. Generally, it is helpful to limit or avoid alcohol, exercise regularly when feasible and consume adequate fluids. Symptoms may be relieved by sleeping with the head of the bed raised.