I do not know about the pilots protocol
but in QCC, we all know if you just so much as mention the word
"fatigue"
to your team manager about yourself or your work colleague, you will be put on a watch list and so will your work colleague and when the opportunity arise, courtesy of team manager's spies on board : your work colleagues also will see that they dob you in on a whole range of things and then of course, the clause 11 will be handed out to you like lollies.
friend of mine got a medical certificate for fatigue, yanked in for 40 questions
then 1 month later clause 11 for totally unrelated matters to fatigue, to dismiss any suspicion.