I love my 92-year-old Dad, but he complains about all his health ailments in the same way. How to know when it is really serious if he talks about everything the same way?

Well, ths short answer is it will be very hard, and you and the medical folks will not be able to rely on his history or reporting of symptoms. Some of us are used to that though - I'm in pediatrics lots of our patients etiher never verbalize or are way off the mark in how they describe things. You may want to give a heads up to any new nurse or doctor though that this is the case with dad.

A shift in your perceptions is necessary. His mind is wearing out. Different functioning; it is the OPPOSITE of having a dream that seems real, then you wake up and realize the weirdness is not something you have to deal with. This, you have to deal with: you have your own reality, and you have your Dad's reality.
After a while, you incorporate this reality into your every day functioning. It becomes easier, once you accept that "it is what it is".
Welcome to the club, and to the site. Good luck, and HUGS,