Really, experience with it has helped me over the years; the more accustomed to it and familiar with it you become, the less you let it get to you.
Otherwise, there's some simple things I've found. When in that bad state of mind there's a tendency to reinforce it in your choice of music; I'd suggest something lively, fun, and upbeat instead. Make yourself eat something light, like cereal and a banana or something of that sort (heavy or high fat foods can make you even more sluggish). Showers can help. Dress yourself with the intent of having some pride in your appearance, as generally randomly chosen baggy clothes meant almost to disguise oneself become the instinctive choice. Open the blinds and make yourself sit in the sun which can be surprisingly invigorating.
If, after doing those things, you feel capable of forcing yourself to exercise, I'd suggest seizing that opportunity as it can help immensely. The above is about all I can think of for "today" that would help me in the short term.
Otherwise, what worked for me over about 12 years of dealing with it was medication. I learned that I had manic tendencies and, once someone finally decided to investigate my blood chemistry, it was discovered that I had the natural testosterone levels of a fairly old senior citizen (I'd highly suggest looking into hormones before trying antidepressants, as they may be entirely unneeded). Having treated the hormones and settled on a couple of less serious, low dose antidepressants, I'd say the difference is night and day.
Just something to maybe consider looking into in the future. Often, though, doing all of those little things I mentioned and establishing routine are enough to really help you get control of your life. Good luck with your exams! :)