A person who walks around and performs activities while asleep, often with no memory of doing so when they wake up.
Compound word: 'sleep' (from Old English 'slæp') + 'walker' (one who walks). The phenomenon was known since ancient times, but the term 'sleepwalker' became standardized in English in the 1800s as sleep science developed. The condition is medically called 'somnambulism'.
Sleepwalkers are actually caught between two brain states—their movement centers are awake but their conscious awareness is offline, which is why they can navigate rooms but have no memory afterward. Some sleepwalkers can even unlock doors or climb stairs safely, showing that the brain's survival instincts never fully sleep!
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