Getting up too quickly causes head rush, and the hot water doesn't help, because that makes you a bit dehydrated. Be sure to drink plenty of fluids after a hot bath/shower.
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Definition
Orthostatic
hypo tension is an abnormal decrease in blood pressure when a person stands up. This may lead to
fainting.
Description
When a person stands upright, a certain amount of blood normally pools in the veins of the ankles and legs. This pooling means that there is slightly less blood for the heart to pump and causes a drop in blood pressure. Usually, the body responds to this drop so quickly, a person is unaware of the change. The brain tells the blood vessels to constrict so they have less capacity to carry blood, and at the same time tells the heart to beat faster and harder. These responses last for a very brief time. If the body's response to a change in vertical position is slow or absent, the result is orthostatic hypotension. It is not a true disease, but the inability to regulate blood pressure quickly."