Final answer:
Syncope following a sudden change from lying down to standing up is due to orthostatic hypotension. Causes include hypovolemia from dehydration or medication effects, and autonomic failure from conditions like diabetes. Treatment involves managing the underlying cause and may include increasing fluid and salt intake.
Step-by-step explanation:
Following a sudden change of posture from the recumbent to the erect position, the patient may experience syncope due to a condition known as orthostatic hypotension. This occurs when there is insufficient blood flow to the brain upon standing, leading to symptoms such as dizziness or fainting. One of the reasons for this condition is hypovolemia, which can be caused by dehydration or certain medications like diuretics or vasodilators.
Another underlying cause of orthostatic hypotension is autonomic failure, where disorders such as diabetes or multiple system atrophy impair the sympathetic activity necessary to maintain blood pressure upon changes in body position. Measures such as increasing fluid and salt intake to improve hypovolemia, or managing blood glucose levels in diabetes, can help counteract the effects of orthostatic hypotension.