In 2002, I experienced what I would term cumulative fatigue even under 'peace time' conditions. Several long UK-Calgary instructional trips interspersed with AAR instructional flights in the UK, simulators, course management niff-naff all due to the 'Won't say no' attitude of the kids in high places masquerading as senior officers conspired to wear me out. To the extent that, having hopped back into the seat just before TOD to act as handling pilot (that leg required the LHS pilot to be non-handling) after a long night Atlantic pond-hop, I got so far behind the jet that I wasn't able to sort out the student navigator's cock-up TOD call (staff navigator hadn't bothered to check it....) and, as a result, we were very hot and high and I ended up having to go around from a rubbish approach. Why had I got into this sitch? Well, apart from forgetting about diurnal effect and not being alert enough to do the (3 x height split plus 10) cross-check, I was basically completely knackered, made wrong calls ("Flap T/O" instead of "Landing Gear down") due to brain dump and simply wasn't working properly....
The only time you know you're too fatigued is when something happens - it creeps up on you insidiously.
In my case, there were 'no wrecks, nobody drownded' (as the saying goes). But no sympathy whatever from the wheels - I later worked out the actual number of days rest I'd had in 3 months and told the 'management' that they needed to think again about their absurd policy of never saying no to ever more stupid demands from on high. Did they do anything? Did they hell - so I then took the decision to leave them to it, pulled the B&Y and got a life again.
Even in civilian, non-flying roles you can get fatigued. I used to work a full week in Europe, getting up daily at 0630 and working from 0800-1800. Then, on the last day, flying to FRA after 1700, then eventually getting to BHX at 2230 (or 2330 'body time'). Home in the dark, arriving at about 0030. After one such 19 hr day, the TV news reported the sad accident which happened to the chap who fell asleep and drove onto the railway lines causing a disaster. I decided there and then that I wouldn't do any more 19 hour days, so nowadays I stay an extra night and have a relaxing journey home instead. It's a lot safer.
The modern world is a high pressure environment and people are often far too eager to please, whether in military, aviation or other spheres. Supervisors must respect the rights of subordinates to say "NO!" to unreasonably fatiguing work demands.
As for the pratt who once said that "Post-route stand-down doesn't apply to Sqn Execs....."
Fortunately he's no longer inflicting himself on anyone in the RAF.