Something I discovered within the past year is that if I know a song fairly well, I can "play it" silently in my head, and be entertained. The experience isn't quite as emotionally resonate as listening with headphones, but it's not so far off either. It's useful when I'm bored. ...can anyone else do this? I actually find it supremely weird.
Edit: I've also had vivid hypnagogic visual hallucinations intentionally. It's a kind of fun game to play, seeing my bedroom clearly with my eyes closed, or checking the time on my watch while same. Obviously I'm conscious and aware that I'm not really checking the actual time, but not particularly surprisingly I'm pretty close since I tend to wake about the same time every day.