i've had that experience... i think its your equalibrium balancing itself out... for example.. you're all hopp'd up on coke, your librium is high on euphoria... then you stop doing it and within some time you're crashing down to the same high but on the negative side, eventually you bounce back to the middle and feel normal again... that goes for alcohol, dope, coke, and anything else that makes you feel wonders... i'll call it the rollercoaster effect