If a person takes a cosmos-tearing dosage (the ones which cause complete panic) while on an MDMA peak, he/or she will be temporarily disconnected from the bliss. From what I've seen (and been through), MDMA won't save one from the fear, but it can synergise a positive experience quite nicely.
different receptor systems, and Salvia has no affinity for the serotonergic receptors which the PEA's and Tryptamines seem to have in abundance.