<unk>  is a poorly understood autonomic disturbance, which manifests as a change in Heart Rate>30BPM upon the patient standing erect from supine or a head-up tilt without underlying<unk>  hypotension. Sympathetic hyperstimulation secondary to a fall in vascular tone and cerebral hypoperfusion leads to transient symptoms such as inappropriate sinus<unk> , chronic fatigue and dizziness. Many patients also report non specific symptoms such as GI disturbances and sleep disturbances. This incapacitating syndrome has no known etiology, with theories listing post infectious, autoimmune, cardiac deconditioning and emotional states as possible factors. Antinuclear antibodies along with elevated ganglionic, adrenergic, and muscarinic acetylcholine receptor antibodies have all been reported. Diagnosis involves eliminating all primary cardiac, endocrine, neuropathic and psychiatric causes of<unk><unk> . Treatment is multimodal and consists of patient education, volume replenishment, physical countermaneuvers (graded stockings) and pharmacological therapy.
Postural orthostatic tachycardia syndrome
Heat syncope
Vasovagal syncope
Neurocardiogenic syncope
Defecation syncope
Micturation syncope
Serotonin syndrome
Cholinergic crisis