i may be mistaking... but when you go on a binge - or whatever you might call it... for few weeks or months or how ever long..
and then stop using - your chemicals do get screwey and can cause depression...
thinking its part of withdrawal... just because your brain isn't being flooded with all those goodies... if that might make sense..? can do a couple google searches on withdrawal and depression - depression and addiction... that type of thing...

sorry you feeling bad ...