MDMA Afterglow?

So this is probably something that has been discussed before (and if that's the case feel free to point me to the correct thread or resource) but I was curious if anyone has found a biological explanation for the MDMA "afterglow" that some users tend to experience following a night of moderate use. For example, a dose of 100 mg to start the night with a 50 mg booster at +2:00 for a 170 lb male tends to leave a positive residual "buzz" for up to a week or even a month following use. This afterglow seems to be heightened when the MDMA is combined with a moderate amount of seretonorgenic psychedelics (100 - 200 ug of LSD one or two hours before MDMA use or 2 g of cubensis ingested at the same time as the MDMA). I know many users tend to experience mild depression following use so it seems odd that other users report the opposite effect.