500mg in two hours is WAY too much, stating the obvious now I know, a standard dose should be around 120mg for an average person. MDMA can be neurotoxic but I suspect all you have done is depleted your serotonin levels to a point you feel like shit and are now feeling depressed. From what you describe your body is also now having a reaction to the chemicals you put into it, you overdid it. There are natural ways you can help replenish your serotonin and some supplements can help, I suggest you give your body a good rest, eat some fresh fruit and drink plenty of fluids (water) to give your body a cleanse and leave the mollie alone for a few months minimum. I have overdone it myself a few times and felt horrendous for days and like you had problems with being sick, it has in my experience though passed. If you are in real trouble though see a doctor.