Plently of people try to stop taking their anti-depressants and face that. It seems like for you, you can either run of the risk of getting SS by staying on the meds or potentially get SSRI discontinuation syndrome if you stop. However, I can say out of the two of those things SS would be a lot worse, if you do happen to get SS you won't be able to take your prestiq (actually an SNRI) for at least several months or very possibly a couple years (or pretty much all other drugs for that matter). If you experience SSRI discontinuation syndrome your symptoms will only last until you go back onto your meds. Overall, SS is more harmful in terms of nerve cell damage, and damages to your endocrine system. For these reasons I'd say you'd be better off taking the MDMA without your meds; SS is too much to risk. If you plan to continue using your prestiq, SSRI discontinuation system will subside when you choose to do so, just remember not to jump immediately back into after rolling.
The only problem I see here is that the day after you roll you may feel extremely depressed, a combination of being off your meds and the fact that you rolled the day before. Who knows though, many people, especially those who don't use MDMA frequently, feel better than usual the next day. To me that still sounds better than developing SS being that it will be much more temporary, thats why you should just try and get through it without taking them for a couple days after. With all that being said you don't want to allow yourself to be a test dummy, so whatever you choose to do, please consider all the factors. Hopefully someone around here who takes anti-depressant can advice you as to what to do as well.