I've been recently reading about hypnosis and I'm asking this question because I've had certain personal experiences that makes me confuse the term Trance with just simple sleep. 

I'm not a fan of Heavy Metal music, but I sometimes listen to it because it somehow calms me down and I usually listen to music while wearing my big uncomfortable headphone, sitting in my chair which is also very uncomfortable and having my legs resting on my desk. When I listen to music, I almost always start to imagine things, for example I sometimes try to imagine a trip to a certain place, or I try to make up a music video for that tune in my mind. The reason why I mentioned Heavy Metal is that, when I listen to that kind of music in that uncomfortable position, I fell asleep in a way that I can still hear the music and this goes on until the whole album is finished and when I wake up I feel really really fresh like my brain has been fully reset. However, this feeling does not happen when I just go to bed or I just get some rest. 

What I have read about hypnosis suggests a similar condition, which is when someone is between being conscious and unconscious (or I can't describe it well). However, the videos I have seen about it emphasis on comfort. Would this be (what's I'm experiencing) a kind of trance or hypnosis, or it is just a normal nap? 

And would there be any reason why a music full of violence, yelling, and rough sounds would calm down the brain and put it into a semi-conscious state and then makes it very refreshed afterwards?