What is the word for repeating an act over and over to the point of insanity?

Question

I don't recall that word but there is a very commonly used word for that if I recall correctly. What is it?

Answer 1

It doesn't apply to insanity specifically (although it doesn't exclude it as a result), but a common phrase is ad nauseam:

[Merriam-Webster]
: to a sickening or excessive degree
// a topic that has been discussed and analyzed ad nauseam

It can apply to both the repetition of an act as well as to the prolongation of a single act. It's an adverb that modifies something in context.