…but psychedelics also effect your serotonin. so wouldnt taking a psychedelic worsen any damage that could have been done?
The action of MDMA and psychedelics are slightly different (MDMA works on serotonin in general, whereas psychedelics work on a serotonin sub-receptor), so the cross-tolerance is surprisingly minimal. I can say this from experience.
Taking any drug (apart from maybe weed) the day after rolling is going to continue to put stress on your body and prevent full recovery. But in events like festivals where you want to take drugs multiple days in a row, you find the safest way to do so.