My homeopath explained it this way after I had a period of very stressful things happen.  She said we all have a "vital force".  As these "bad" things happen, they are like punches to our vital force.  When it's a lot in a small amount of time, it's hard for the vital force to recover in between punches and basically it drains us.  For me, I went into a deep depression and didn't even realize it.  I'd never had depression before, but after all the "punches", I just sort of fell apart.
I'm fine now, it was in 2010, but I had to take action and take care of myself to get well.   2011 ended up being the best year ever.
I hope you feel better.  If you haven't tried homeopathic medicine, look into it, or at least check out integrated medical care which uses east and west medicine to treat the patient, Dr. Andrew Weil is a famous integrated medical doctor, for example.