Never Wake a Sleepwalker
"The warning that waking someone mid-sleepwalk can cause them serious harm, even a heart attack."
Major medical bodies, including the Mayo Clinic and the American Academy of Sleep Medicine, are direct on this: waking a sleepwalker doesn't cause heart attacks, brain damage, or any comparable medical harm. The belief has genuinely old roots, though, tracing to 12th and 13th century ideas that a person's soul temporarily left their body during sleep, so waking them abruptly was thought to risk trapping it outside. The real, far more mundane reason people still avoid it: a woken sleepwalker is often confused and disoriented, which can occasionally lead to a minor accidental injury, nothing supernatural about it.