Depression has hit me like a ton on bricks

I can say from experience that it is basically a waiting game. You don't really have control over it and you're just gonna have to stick it out. It's horrible, especially when it has got to this level. Don't try and think about exams, perhaps ask a friend to let someone at uni know what's going on.
Just remember, you have time. This time of year is often a bad time for people with depression, and unfortunately its just something you have to get through. Although its hard to accept, you'll come out of it and things will look up. You won't feel like doing anything or eating anything or even moving, I know, but perhaps ask a good friend to come round and maybe even just sit with you? Just ask, people will want to help. Or at least let someone know what's going on - that's essential.Talking can sometimes help, but when things get this bad you don't want to dwell on the bad things.
Take a few days to do absolutely **** all and forget everything and all the stress. The first thing I'd suggest would be to listen to some music, and build up from there. Music has a big impact on your mood and even if you start with music that reflects your current feelings, you might remember a song you used to like or a song that has a slightly 'lighter' sound. Build up, maybe grab a brew, and a cig if you smoke. Try and steer clear of the alcohol until you feel up to socialising with your friends.
As long as someone knows, there's no need to worry. As soon as you've listened to music, had a brew, let someone know, had a friend over, maybe talked if you've felt like it, you should maybe work up to making some easy plans, something you'll enjoy. I know you don't wanna do anything right know, but you will in time :] Invite a couple of friends round, and then a few days later maybe have five :] Then perhaps go for a coffee with a friend if you feel you can be arsed to go out haha :] Even keep chatting on this thread until the weight lifts a little :]
As soon as you can, distract yourself. It's key. And the thing to remember is that you're strong, you can deal with this, and nothing stays the same forever. It's very important not to think about uni or whatever, because it's not important in the grand scheme of things really, at least for now. You'll pull through. You've obviously done it before, and there are loads of people out there waiting to help. Don't lose faith, smile if you can, even if it's fake :] I believe you can get through this, and I know you will :] xx

More caffeine and 1 hour exercise every day. For at least a week.

I'm completely serious.

Report back when you're happy.