Meth and E are definitely not the same the thing. If it is good E, it will be mostly made of MDMA, whic if used responsibly wont have many bad side effects. In high doses it can cause some naseua, and you might find yourself grinding your teeth a lot, especially if you are dancing. Chewing gum is a good way to avoid that.
Make sure you drink water so you dont get dehydrated but if you drink too much water you can get hyponatremia, which just means your salt level is dangerously low whoch can be VERY bad. So eat some salty snacks or just drink gatorade.
Come down can be pretty uncomfortable and people have all sorts of remdies for that, most of which involve more drugs.
The worst part, imo, doesnt show up for about 2 days after use. That is when the 'hangover' starts. Basically just a minor depression due to seratonin depletion.
The problem is it isnt a regulated substance and you will most likely not be getting pure MDMA. E pills have been known to contain 2C-I, 2C-B, Heroin, Cocaine, MDA, Meth, PCP and DXM just to name a few, and will often have no MDMA in them at all. This where the really bad side effects come into play.