Hello! Fellow music lover (and part-time writer/performer) here and somebody who tends to bottle up emotions if I don't work at it, with people I trust, or through music...

If you listened to happy music all the time, to try and mask what you are really feeling, I tend to think that would then be short-circuiting the process? You get people who try to be positive immediately, and they bottle up their negative feelings, sometimes for years, only for those negative feelings to crop up again when they've forgotten why... It's better to work through the negative emotions, and process them, before then using positivity to look for the good in the situation and what opportunities you may have missed when you were too sad to see them.

I hope this helps... your preference in music may be telling you where you are right now. If you've been sad for months or years, hopefully you can find the support you need and find the root causes of it, and slowly fight your way back up... at first you might only have the energy for a little bit at a time, but it starts to pay off in interest!