Oddbean new post about login | logout Aural hallucinations at the onset of sleep are very common. Just chuckle at how real it sounded, then go back to sleep.
Then again, search the Internet and find all the things it can be associated with. That will freak you out and you'll probably therefore hear more of them in the future! Generally if you are under greater mental stress recently, of any kind (including the aforementioned onset of schizophrenia, or generalized anxiety, or sleep disorders, or anything causing mental stress and mental hyper novelty even for example sleeping somewhere new) they will be more common.