Jaw clenching caused as a side-effect of consuming LSD. Generally not dangerous. Treated by staying hydrated and exercising the mouth. Nothing to worry about as worrying can cause a bad trip.
Luke: You just gotta watch out for The Clench
A.J. (On LSD): The Clench? Wtf is that?
Luke: You don't know about The Clench man? That shit will lock your mouth shut!