strange display turning off issues?

[haiaiai]

My 15in Macbook Pro '13 (obtained new late '14 on B&H, started using it early '15) has a display that randomly turns off (dim backlight is still on - I can see the slight difference when I actually power the laptop off), in addition to the programs (audio abruptly stops, etc.). The computer is still "on" (humming, backlight on) and it'll overheat after a bit; I must hold power to reboot. Potential issues resolutions?

Other things -

1. it happens in bursts, i.e. happens once, and if I do the rebooting thing and continue with using it, most likely it'll happen again within 10 minutes or so, and if I keep doing it, at some point it'll turn off almost immediately after I log in (but never before! ?? idk...)
2. Seems like CPU-consuming tasks cause it to happen more frequently - however, I've never had it happen once during a vidchat on Skype or Hangouts, so I don't know?? iTunes makes it more likely to happen though
3. Seems to happen more often on lower battery/not charging, but has recently been happening at times at 100%/plugged in.
4. It's probably hardware - I updated from 10.9 (issue started then, like 2 months ago) to 10.11 and issue continued to occur.
5. I suspected battery, so I went to Apple Store and initial diagnostics found nothing on any front
6. It's been getting worse and worse - happens more frequently and (as mentioned) at higher battery %s. By now I can nearly guarantee an ooccurrence once every 3-4 hours or so of use.
7. No, turning it off and on again doesn't help.

Any help would be appreciated! Thanks :c

MacBook Pro Retina, OS X Yosemite
(also posted on Apple forums but this seems to be more active and helpful... :x)