First of all understand that most of the time depression is beyond yourself. Is a mental disease that needs treatment in order to get better.

I'm sure you don't want to be in this situations, so I'd suggest you to talk with a doctor about this and get some exams, it might be hormonal, emotional, etc; I'm not really sure because I'm not a professional, but the point is that you can get help.

Start by getting out of your room, eating something.. Get a bath, and dress yourself. Take it step by step and make an appointment, just go, be honest and talk it out. It's really normal.

Investigate the subject, and learn as much about it, it could helo you understand it better, start maybe by reading this: http://en.wikipedia.org/wiki/Clinical_depression

Get some tips, support,etc; here:

Link 1
Link 2

Good Luck. :)

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