in guideline Syncope http://purl.obolibrary.org/obo/HP_0001279 SCDO:0008553 Sufficient HP:0001279 Syncope refers 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. Fainting Spell Abnormal Cardiovascular System Physiology National Guideline for the Control and Management of Sickle Cell Disease Sickle Cell Disease: The Clinical Care Guidelines of the Sickle Cell Unit Consensus Statement on the Care of Patients with Sickle Cell Disease in Canada Evidence-Based Management of Sickle Cell Disease