I did a bit of research into it, correct me if im wrong please.
The combination of Effexor and Trazodone can increase serotonin levels in the brain, leading too, rapid heartbeat, high blood pressure, seizures, and comas.
While Seroquel and Trazodone are both central nervous system depressants, taking both of them in high dosages can lead to respiratory depression
ofc it varies person to person, but im pretty sure this mixture is pretty fatal, there's a lot of other things that can happen but from what I looked into that's the main ones.