Extreme mood lift, increase in energy, increase in social outgoingness, acuteness in senses (hearing, touch, sight are much more sensitive than sober). Feelings of love and comfort are more apparent as a MDMA user will explore these emotions more with people around them.
Dehydration, nausea, and jaw clenching are a few negative side effects, but when taking a pure MDMA (Molly) pill it's very less likely for these to occur.