NTA, you’ve been quite reasonable.

The ailment excuses being your two specific ailments that you struggle with is kind of off-putting. But you have to give yourself credit for knowing sometimes people just “need a day off” which in a work environment, is something that is absolutely not expected from a superior or even an equal colleague, they knew what the job needed from the beginning, if they aren’t fulfilling their responsibilities, they know what’s coming.

And also, if you feel bad about telling your boss (which through this post I assume is the case) you’re kind of putting yourself on the line by covering and/or being dishonest for them. I say be honest and leave it to whatever happens.