Advised ones body has hard time regulating blood pressure heart rate etc they think due to nervous system not able to control body functions. Always best to rule out other possible symptom causes and hope this helped

Postural Orthostatic Tachycardia Syndrome
Symptoms related to the reduced blood volume that occurs when standing up.
This syndrome is usually triggered when a person stands up after lying down. It most commonly affects women between the ages of 15 and 50.