Sometimes you gotta just let your body do what it knows best. Most of the time the brain is the problem, especially when you start over thinking. Humans are constantly getting in their own way, which usually translates to diminishing results.
An ongoing debate in the weight training industry is when should one breathe when performing repetitions. Typically the answer is to take a breath at the starting point of the exercise, releasing air throughout the exercise until the repetition is completed, and repeating that same protocol for each repetition performed thereafter until training set is completed.
This advice is sound, but it doesn't necessarily produce the best outcome, because it causes the individual to focus on breathing instead of the exercise. So, what's the solution? One way is through repetition, in this case meaning teaching your body and brain what you want it to do, because repetition is the mother of skill. Let human nature take precedence, in most cases it's the right approach, because your body and brain are innate. In other words, your body and brain by its own nature know what to do, so get out of its way. It knows when to breathe.
The only exception where this wouldn't apply are when bad habits have been learned to begin with, for example if you held your breath throughout the entire repetition or training set. Not only could this inhibit performance, but potentially be dangerous, because of intracranial pressure, otherwise known as pressure around the brain.
Let's be clear, it's not a problem temporarily holding your breathe, just not entirely. An easy way to execute reps and sets without wondering when and where you should breathe is to make sure some air is being released ever so slowly during the exercise. In order to make each repetition a perfect one, you need to focus on the muscle, not your breathing.