Call it the way you want , we are not doctor or health expert...
Call it unfit to fly if you prefer BUT it happen too many times that pilots are flying when not enough rested to perform as they should in an emergency or difficult condition.
The main reason being that the roster is design for single pilot with a maid to do all their cleaning shopping etc... to allow the pilot to just fly , eat and sleep
Only then , their published roster is "duable" without being "tired" , "fatigue" or "unfit" as you prefer to call it.