Orthostatic hypertension, or OH, is a condition characterized by an increase in blood pressure upon standing up. This condition is also known as postural hypertension or positional hypertension. OH can be caused by different factors such as nervous system dysfunction, dehydration, or use of certain medications. In addition, standing for extended periods, especially in hot weather, can exacerbate orthostatic hypertension. Some synonyms for OH include postural hypotension, orthostatic hypotension, and head rush. These terms are used to describe the same condition, but the emphasis is on different aspects of the blood pressure changes that occur when standing up.