There are already great suggestions here I think, and I also echo the medical route if you think it's appropriate. I want to add another possibility, because with a broad enough range of options you might find something quite effective.

It occurs to me you may be under challenged. It seems your academic life comes easy enough for you to simply go through the motions, allowing for listlessness to set in. To remedy that I'd find some challenge to take you out of your comfort zone like a marathon, for example, or trying to master something such as a game/sport or new skill. Done correctly, you won't really have time to stare at a screen for 30 minutes. Find something constructive that interests you. If it's something that scares you (because you may fail) even better. It may just be that you're in a rut and need to be shaken out of it. One thing is for sure: you can't regularly challenge yourself to scary things outside your comfort zone, succeed in such enterprises and remain depressed all the while. At least I sincerely doubt it.

Good luck!