Loss of consciousness

For a lay person:

Loss of consciousness is when a person suddenly or gradually becomes unaware of their surroundings and cannot respond to what's happening around them — even if you shout, shake them, or pinch them. It's like their brain "switches off" temporarily or for a longer time. Common examples include fainting (passing out), being knocked out in a sports injury, or falling into a coma. The person looks unconscious, their eyes may be closed or glazed, and they have no memory of the event afterward.

For a trained medical person:

Loss of consciousness (LOC) is a state of impaired or absent arousal and awareness resulting from disruption of the reticular activating system (RAS) or bilateral cerebral hemispheric dysfunction. It is characterized by:

• Inability to respond purposefully to external stimuli (verbal, tactile, or painful).
• Absence of awareness of self and environment.
• Variable duration, ranging from transient (e.g., syncope, concussion) to prolonged (e.g., coma).

Clinically, it is assessed using tools such as the Glasgow Coma Scale (GCS), AVPU scale, or Full Outline of UnResponsiveness (FOUR) score. Differential includes syncope, seizure, metabolic encephalopathy, structural brain injury, intoxication, or psychogenic causes. True LOC must be distinguished from states of preserved awareness with motor inhibition (e.g., locked-in syndrome) or psychogenic unresponsiveness.