Orthostatic intolerance
Orthostatic intolerance is the failure of the body to properly adjust to an upright position, especially with respect to blood flow, heart rate, and blood pressure.
A common manifestation of chronic orthostatic intolerance is postural orthostatic tachycardia syndrome.
The loss of orthostatic tolerance is also an undesirable consequence of human adaptation to space and has often been emulated in head-down bed rest studies.