I find that not wanting to listen to music - even music which has many happy memories for me (perhaps especially so? Dunno.) - is kinda one of my first indications that I'm about to spiral down into a more rough period. I just can't stand to hear it, for some unquantifiable reason. Just all of a sudden it'll start annoying the hell out of me and I'll rapidly go and turn it off.

There are also some artists/songs which will just make me feel like crud, and I may or may not improve after I stop listening to them. Some songs I can understand why - either the song itself or previous memories associated with it, but others I just don't know why it is they seem to make me feel awful.