I had a wild weekend but feel guilty about having a good time?

It's because you have been taking drugs. Especially ecstasy. Your serotonin levels plummet again once it wears off so you end up feeling bad about yourself and have what is known in Glasgow anyway as "a suicide Tuesday" as that is when the comedown effects of a sat and sun partying are usually felt. I would try and calm it down a bit as it will end up having a detrimental effect on your mental health.