Is fatigue a real possibility if you work when your circadian rhythm (red eyes, night flying, long days, early starts) wants you to be asleep? Yes imho.
Are there ways to mitigate it as mentioned here? Sure but ymmv
I had a fatigue call in 2019 and was suspended w/out pay by my CPO.
Did I expect this? No.
I’m a retired AF guy at a ULCC now so you know, but I’m sure I’ll get donkey punched by some Riddle Rats anyway. Who never served btw.