Hearing (spoilers)
Just a neat little connection I picked up on this, my 20th (or something ridiculous), viewing:
If you flatten out the flashbacks into a linear narrative, you get Mickey and Holly going on an awful date at a rock show after which Mickey complains he's never heard anything so loud and that he jokingly thinks he's lost hearing in an ear.
He does lose his hearing, goes through the tests, the life crisis, etc., which leads him, after making a spiritual breakthrough, back to Holly at the end. Cool non-linear arc.