My brother in law is in the middle of chemo for lung cancer. He may have just had round three. There is a pattern - first week, wiped out, just very tired. Then he starts to get better, goes back to work, eats a lot - right back to normal for the next two weeks. Then another round. Your dad will be fine.
The dr.’s are going to give Dad chemo treatments once a week rather than once every three weeks, I guess because of his age (he’s 84). They said they’ll use smaller dosages this way and it shouldn’t knock him down as hard. I just hope he’s able to have some good days each week before going back in for the next treatment.
I hope your brother-in-law responds well to his treatments.