Medical term for sleepwalking. In everyday conversation, 夢遊病 is understood but 睡眠時遊行症 (すいみんじゆうこうしょう) is the more formal clinical term, and 寝ぼけて歩く or 夢遊状態 are sometimes used descriptively.
As a symptom of sleepwalking, one may wander around unconsciously at night.