Category · 3
Presyncope
The feeling of being about to faint — light-headed, with greying vision — but without losing consciousness. Its danger is being mistaken for vertigo and delaying a cardiac diagnosis.
A perfusion problem, not a vestibular one
Presyncope is the “about to pass out” feeling — light-headedness, greying or tunnelling vision, sometimes a thumping heart or sweating. It happens when the brain briefly doesn't get enough blood, most often on standing up.
It usually comes on with standing or exertion and eases on lying down — the opposite of inner-ear vertigo. Recognising it matters because some causes are dangerous heart-rhythm problems.
Presyncope is near-faint without loss of consciousness, from transient cerebral hypoperfusion. The big three causes are orthostatic hypotension, vasovagal syncope, and cardiac arrhythmia. Orthostatic hypotension — a sustained fall of ≥20 mmHg systolic or ≥10 mmHg diastolic within three minutes of standing — is especially common in the elderly and on antihypertensives; work-up is lying/standing BP, ECG, and, if needed, tilt-table testing.1
Vasovagal episodes are reflex-mediated (vagal overactivity, sympathetic withdrawal) and provoked by emotional stress, pain, or prolonged standing; physical counter-pressure manoeuvres help.3 The non-negotiable step is excluding cardiac syncope — brady- and tachyarrhythmias, structural disease, or a suspicious ECG — because mislabelling presyncope as vertigo can defer the diagnosis of a life-threatening arrhythmia.2
- About to faint / black out
Ask“Do you feel as though you're about to pass out, with greying or dimming vision?”
Presyncope from transient cerebral hypoperfusion — not vestibular.
Orthostatic hypotensionVasovagal syncopeArrhythmia - Worse on standing
Ask“Does it come on standing or after exertion, and ease on lying down?”
Orthostatic hypotension — check lying and standing blood pressure.
Orthostatic hypotension - Palpitations / exertional▲ red flag
Ask“With palpitations, chest discomfort, or onset during exertion?”
Possible cardiac cause — exclude arrhythmia and structural disease (ECG).
Arrhythmia