mdma can cause you feeling a bit out of it for the next few days and can trigger anxiety if you're prone to that (especially if you had a lot of stress lately). mda is even worse in that respect. i've been in a slightly dizzy, anxious, slightly "psychedelic" state for two to three weeks after my first time of mda.
the most important things to remember (besides of course getting your stuff tested before tasting it!) imho are:
-it's not neurotoxicity.
-it will go away.
things i've found to help are calming down, relaxing, getting enough sleep and to a lesser degree eating healthy.
if you have trouble with calming down and sleeping well (you're most likely to), benzos help a lot. if i'm in that situation and take some bromazepam to combat the anxiety, it cuts down the time needed to feel normal again from 1-4 weeks to 3-7 days. just be sure not to take them too long and when you stop then taper down your dose.