Older adults are more likely to have orthostatic and postprandial hypotension. Children and young adults are more likely to have neurally mediated hypotension.
People who become dehydrated or volume depleted due to many reasons are at risk for hypotension.
People who take certain medicines, such as high blood pressure medicines, are at higher risk for low blood pressure. People who have central nervous system disorders (such as Parkinson's disease) or some heart conditions also are at higher risk for low blood pressure.
Other risk factors for hypotension include being immobile (not being able to move around very much) for long periods and pregnancy. Hypotension during pregnancy is normal and goes away after birth.
This answer from the National Heart, Lung and Blood Institute has been reviewed and/or edited by Dr. William D. Knopf.