It's a repetitively iterated requirement* and the leaders lead by example. Perfectly normal people in that environment are going to pick it up osmotically. They don't need a mental disorder up front. That isn't to say that the cognitive dissonance of lying in the name of "Truth" won't lead to psychological problems.
Perfectly intelligent and otherwise normal people in the Pentecostal movement can convince themselves that the repetitive babble they spout is some sort of true language gifted to them by the Holy Spirit.
In the end, you run with what the group pressure tells you is right.
* Being a bit hyperbolic here.