Yes, there is a very high risk of serotonin syndrome with mixing DXM, SSRI's, psychedelics, high dose tramadol, and MDMA. Mixing any of the two can cause serious serotonin syndrome. Even if you don't die of hyperthermia or a seizure, you mght have an extremely uncomfortable trip, full of overheating, sometimes violent agitation, confusion, blacking out, and serious irritability.
AVOID THE COMBINATION AT ALL COSTS!!!