Predictability is key. We do hub turns and they are relatively predictable. I have to plan sleep and exercise a little bit, but it’s not bad. For one of our customers, our company consistently builds lines where pilots fly during the day one day, all night the next, the day after, back to nights, etc. Those are a little worse, but also still manageable since you can still anticipate things.

When schedules change every couple hours planning rest and exercise becomes very difficult.

Ok then, let me rephrase this to be more specific about Fatigue.
How many folks are calling in fatigued ? How many of you have made a fatigue call ? Does making a fatigue call make a difference ? Is anyone fearful of making a fatigue call ?

Simply it is this:

"If you can't stand the heat, stay out of the kitchen"

Fatigue is part of flying - deal with it.

Of course you could do what 99% of crews do - hope & wait for the Captain to call in fatigued.

I have made the call a handful of times in 22 years of professional flying. At the part 135 job I had, it made you pretty unpopular. I was even reprimanded once for not telling our scheduling/dispatch sooner that I was going to be fatigued. But under 121 with a FRMP, there is no fear of making a fatigue call unless you're doing it frequently, in which case you're either abusing the program or not adjusting properly to the requirements of the job.

15 yrs of 121 flying and only a few fatigue calls. Absolutely no questions whatsoever. On one call the duty officer wanted to know why I didn't call earlier.

How about you answer your own questions first... then perhaps you will get some responses.....

Fatigue management is part of the job and has wide range of solutions.
I sleep when and where I can, avoid caffeine and garbage foods and work out whenever possible.

Some folks take vitamin c supplements, others take melatonin (or something similar) to regulate sleep cycles.

If fatigue is a problem, that part of the industry might not be for you.

I am writing a research paper at my university about pilot fatigue. I would like to ask you to fill in a really short survey for my research.
It takes less than 2 minutes and would be a great help. Thanks in advance.

https://forms.gle/5GSgDJfcvDZDbDJq8

Also would be interested if anyone has any experience with SAD lights or bright light therapy to help waking up more easily or to sleeping better.

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.

You can only get donkey punched if you let them take you from behind in the first place, but hey, if that's how you like to spend your layovers, that's your prerogative.