What causes some folks who used to be logical sensible reasonable to go off the deep end qnd turn intpo wackadoodles? Is it mental?

Dental? Oriental? Continental? Coincidental?  Is it one thing or a zillion? Is it a communicable disease that is incurable? Now you him/her now you don't "What happened to you?" Do you ever ask or do you not bother since they will lie to you probably anyway? Is it endemic or an epidemic/pandemic?