I have a couple.
1. Sumotori Dreams: This one sorta holds a special place for me because it basically let me keep my sanity when I was sick from taking Prednisone, which I just call the Nightmare Pill now. Do you know what "paradoxical insomnia" is? Neither did I. And then I took THAT. Suddenly, I learned. Among all sorts of other things that went horribly wrong for a freaking MONTH. I was too screwed up to do all that much in the way of complicated gaming, so a huge portion of what gaming I did do was just this one game. Such an incredibly simple little game, but it can be hilarious, and is just meant to mess around and see those guys just trip and fall all over the place and go through floors and whatnot. You'd have to look it up to see just what the game is like, it's hard to explain.
2. Goat Simulator: I'm in a bad mood? GOATS TO THE RESCUE. Seriously, it's hard, very hard, to STAY in a bad mood after playing this one. It's just... so damn hilarious. Mods make it even more hilarious. I've put who knows how many hours into this, and I still find new and unexpected bits of complete, wonderfully glitchy hilarity in this. The devs have done a good job supporting it thus far, too, with 2 large expansions to it (which were free).
3. Super Smash Bros U: Okay, this one can even distract me from my allergies. As in, it actually shuts it off. I dry up after playing this, thus clearing my sinuses (and the effect remains afterward, too). Every time. No, I dont know how in the hell this makes any sense whatsoever. Frankly, I dont CARE how it makes any sense. It's just another benefit to an already great game. It's hard for anything to bother me much when playing this.
4. Binding of Isaac: Rebirth: ABSURD REPLAY VALUE. You never know just what sort of loopiness will happen on any given run. The game promises hundreds, even thousands of hours of replay value, which it fully delivers on, and there's so much depth to it, and lots of decision-making to do (grabbing the wrong items at the wrong time, based on items you already do or do not have, can end your run really fast, often in a hilarious way), that I just find it freaking impossible to concentrate on things that have been angering me or whatever. It just doesnt get old, and a game not getting old means it can do alot for me, in this manner.