Fainting

Fainting, or syncope, is a transient loss of consciousness caused by a brief global reduction in cerebral blood flow, with spontaneous and complete recovery. The reflex or vasovagal form accounts for the majority: a trigger such as pain, fear, heat, prolonged standing or the sight of blood activates a reflex that slows the heart and dilates blood vessels, dropping blood pressure below what the brain requires. It is typically preceded by a recognisable warning — lightheadedness, nausea, warmth, tunnel vision and sweating — and lying down at that point often aborts the episode. Situational syncope follows coughing, swallowing, urination or defecation. Orthostatic hypotension causes collapse on standing, from dehydration, medication or autonomic failure. The minority that matters most is cardiac syncope: arrhythmias, structural heart disease and outflow obstruction can present identically but carry risk of sudden death. The features that separate it are consistent: syncope during exertion, without any warning, while lying down, with palpitations, or against a family history of sudden death before 50. Any of those converts a faint into a cardiac workup. A first faint in a young person with classic triggers usually needs only reassurance; recurrent or atypical episodes do not.

• •Preceding lightheadedness, nausea, warmth and sweating — the classic vasovagal warning
• •Tunnel or greying vision and fading hearing
• •Brief unconsciousness, usually under 20-30 seconds
• •A few jerking movements that mimic seizure but reflect hypoxia
• •Rapid, complete recovery within minutes in benign causes
• •Collapse without warning, during exertion, or with palpitations — cardiac red flags
• •Prolonged confusion or tongue biting suggesting seizure instead

• •Vasovagal reflex: pain, fear, heat, prolonged standing, blood or medical procedures
• •Dehydration and inadequate salt and fluid intake
• •Standing quickly, particularly with antihypertensives, diuretics or in older age
• •Situational triggers: coughing, swallowing, urination, defecation
• •Arrhythmias, both fast and slow
• •Structural heart disease: aortic stenosis, cardiomyopathy
• •Postural tachycardia syndrome and autonomic dysfunction
• •Hypoglycaemia and anaemia as contributing states
• •Prolonged bed rest and deconditioning
• •Pregnancy, through venodilation and inferior caval compression

Vasovagal syncope is a reflex arc: afferent triggers stimulate vagal output and withdraw sympathetic tone, causing bradycardia and vasodilation that drop cerebral perfusion. Orthostatic syncope results from inadequate vasoconstriction on standing, whether from volume depletion, antihypertensives or autonomic neuropathy. Cardiac syncope results from arrhythmia or structural obstruction abruptly cutting cardiac output. All share the final common pathway of transient cerebral hypoperfusion.