Pertaining to the posture or position of the body, the attitude or carriage of the body as a whole, or the position of the limbs (the arms and legs). Postural hypotension is a drop in blood pressure ( hypotension ) due to a change in body position (a change in posture). It occurs when a person, often an older person, moves to a more vertical position: from sitting to standing or from lying down to sitting or standing. The change in posture causes a temporary reduction in blood flow and therefore a shortage of oxygen to the brain, which leads to lightheadedness and, sometimes, a "black out" episode, a loss of consciousness. See the entire definition of Postural