see go off the deep end.
The American Heritage® Idioms Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.
Examples from the Web for deep end
Also known as The Abstinence-Violation Effect, some individuals can feel an overall loss of control after going off the deep-end.When Is It OK to Cheat? The Pros and Cons of Cheat Days
July 14, 2014