Sleepless refers to someone who hasn't slept or hasn't had much sleep.
When people are awake all night and can't stop thinking about something, they often describe themselves as being sleepless. This usually happens when there's a big exam coming up, or you're waiting for news from someone important, like a doctor after some tests.
Characterized by an absence of sleep: wakeful.
Example: I spent a sleepless night worrying about the exams.
