Stress release bomb in my head...?

I've been curious about this for some time now.  I went through a pretty bad stage of depression that lasted somewhere near two years.  I'm still recovering from it and have to be very cautious about my well being.  However, whilst at my worst I experienced something rather unusual, when I was, only what I can describe as; feeling the most awful I could ever imagine feeling and just when I felt it was too much to bear, a particularly strange thing would happen.  There seemed to be a release of some chemical or another and I'd instantly relax and feel better.  The effects only lasted a couple of hours but I'm sure this stopped me having a heart attack or something.  Does anyone know what happened here.  I'm a biomed (That is NOT a Dr) and am looking for some insight into what this neurotransmitter is?  Any ideas?  Can't find anything online about it.  

[Alisonj29]

I wish I had an answer for you and hope that someone here does. I would be very curious to here what it could possibly be. I would love to have something release and be able to instantly relax