MDMA comedown, advice anyone?

You should always preload with 5-HTP and I'm guessing you didn't do so. You can try post-load, go get 5-HTP from GNC, the drugstore or health store. Take 2 capsules 4 to 5 times a day for a few days to help get your Serotonin back in balance. Eat a little chocolate, stay hydrated and get enough sleep. You should be feeling better shortly.