<unk>  is a condition of dysautonomia, and more specifically,<unk>  intolerance, in which a change from the supine position to an upright position causes an abnormally large increase in heart rate, called<unk> .  This is often, but not always, accompanied by a fall in blood pressure. Patients with<unk>  have problems maintaining homeostasis when changing position, i.e. moving from one chair to another or reaching above their heads. Many patients also experience symptoms when stationary or even while lying down. Symptoms present in various degrees of severity depending on the patient.<unk>  is a serious, though non-life threatening, medical condition that can be severely disabling and debilitating. Many patients are unable to attend school or work, and especially severe cases can completely incapacitate the patient.
Postural orthostatic tachycardia syndrome
Heat syncope
Vasovagal syncope
Neurocardiogenic syncope
Defecation syncope
Micturation syncope
Serotonin syndrome
Cholinergic crisis