Hi the symptoms could be because of orthodtatic hypotension Orthostatic hypotension is defined as a decrease in systolic blood pressure of 20 mm Hg or a decrease in diastolic blood pressure of 10 mm Hg within three minutes of standing when compared with blood pressure from the sitting or supine position. so The most common symptom of orthostatic hypotension is feeling lightheaded or dizzy when you stand up after sitting or lying down. This feeling, and other symptoms, usually happens shortly after standing up and generally for few seconds conpression stocking should be used posture should not be changed suddenly keep him hydrated investigation adv carotid doppler hutt test electrolyte disbalance thanks consult your doctor soon