Postural orthostatic tachycardia syndrome
It is defined as a syndrome in which people develop dizziness upon standing up in the absence of heart or other structural disease.
This dizziness is associated with a rise in heart rate (usually an increase of thirty beats per minute) without a drop in blood pressure.
Besides dizziness, the symptoms often include lightheadedness, weakness, palpitations, difficulty concentrating, and headache. Other symptoms may include flushing, blurred vision, a tremulous feeling, and chest discomfort.