What we (industry wide) need is some standard phone call that can be made. E.g. "I am not fit for duty". End of story, no questions asked.
We should not need to explain if it is a blocked sinus or an 18 month old baby screaming all night that has prevented sleep.
As it is, when sick, there is no requirement to disclose the nature of the illness, and this should be the same for fatigue. Should be illegal to question it whatsoever.
I've had ops guys arguing on the company frequency about subsequent sectors that I said I would not be fit to fly for. Not cool when already on an extended duty, flying straight at the rising sun.