Rare diseases · Sign or symptom
Syncope
Fainting spell
HP:0001279
What it means
A transient loss of consciousness (i.e., characterized by a rapid onset, a short duration, and a spontaneous and complete recovery) due to cerebral hypoperfusion.
Syncope is a syndrome in which loss of consciousness is of relatively sudden onset, temporary (usually less than 1 to 2 minutes), self-terminating, and of usually rapid recovery. Syncope leads to a generalized weakness of muscles with loss of postural tone, inability to stand upright, and loss of consciousness. Once the patient is in a horizontal position, blood flow to the brain is no longer hindered by gravitation and consciousness is regained. Unconsciousness usually lasts for seconds to minutes. Headache and drowsiness (which usually follow seizures) do not follow a syncopal attack. Syncope results from a sudden impairment of brain metabolism usually due to a reduction in cerebral blood flow.
In everyday care
Most people with this sign do not have a rare disease — it appears in common conditions far more often. These general reference pages cover the same topic:
Rare diseases that can present with this54
Common30–79%
14- Brugada syndrome
- Dopamine beta-hydroxylase deficiency
- Familial dilated cardiomyopathy with conduction defect due to LMNA mutation
- Familial idiopathic dilatation of the right atrium
- Glycogen storage disease due to muscle and heart glycogen synthase deficiency
- Hereditary atrial fibrillation
- Hereditary pheochromocytoma-paraganglioma
- Hereditary progressive cardiac conduction defect
- Idiopathic pulmonary arterial hypertension
- Isolated congenital long QT syndrome
- Jervell and Lange-Nielsen syndrome
- Pure autonomic failure
- Sporadic pheochromocytoma/secreting paraganglioma
- Supravalvular aortic stenosis
Sometimes5–29%
27- Acquired aneurysmal subarachnoid hemorrhage
- Acquired methemoglobinemia
- AL amyloidosis
- Atrial septal defect, ostium primum type
- Autosomal dominant hyperinsulinism due to Kir6.2 deficiency
- Autosomal dominant hyperinsulinism due to SUR1 deficiency
- Cardiac diverticulum
- Catecholaminergic polymorphic ventricular tachycardia
and 19 more in this range
The range is how often this sign appears among people diagnosed with each disease — it is not a probability of having any of them. Many of these signs also occur in common, non-rare conditions. A sign on this page is a conversation to have with a clinician, not a conclusion.
Part of the broader category
Tracking symptoms like this for someone? Eleplan keeps symptoms, diagnoses, medications and every specialist in one plan.
Start free with EleplanThis page uses the Human Phenotype Ontology (2026-06-23) — Human Phenotype Ontology Consortium, hpo.jax.org. Disease associations from Orphanet (INSERM), CC BY 4.0. Content is educational and is not medical advice.