^ I've picked up a pretty bad smoking habit over the past year or so and found that on the days I'm really bummed, smoking either makes or breaks that mood for me, I either forget about all my worries as I realize how insignificant they really are or start becoming paranoid that I'm actually genuinely in the process of fucking my life up (when at my worst, which is rare). I usually just try and keep myself busy with work and tasks till my brain just rides it out; finding something to do will distract your focus from what bums you out as you concentrate on something. I'd recommend something creative you can just let flow out of yourself and then it's pretty much a meditation session. Go skate if you can, preferably in a non-stressful environment (solo sessions can be amazing in such instances).
I also used to really hate naps because they would fuck up my sleep schedule and I think waking up in the middle of the day is the worst (and it always makes me feel like shit), but over the past month or so I've become an adept and can confirm that they really work as a reset button of sorts, most of the time you really only need twenty minutes and those will do wonders.