If you was to eat a Pill containing MDMA then eat one containing DXM i'd say it would cause serotonin syndrome and be fatal.
Please test your pills using a Reagent test kit, such as a marquis (They come in many varieties)
Without testing them, you don't really know for sure what is in them.
I suggest you look at the Ecstasy Data results page to give you an idea of some of the adulterants that end up in pills.