Luckily I haven't been in a band that had to play 4 hours since the 80's.. But, even then we had people that hauled all the equipment, set it up, tore it down etc.. and we played 3-5 days in the same town, so a LOT less physical work off stage..
Right now, as I've mentioned, it takes me 2-3 months of busting my butt to do the production for a show.. We only play Sat nights, but I run my butt off from 7am FRIDAY morning until about 5am Sunday morning.. that includes the mother of all setups, since we no longer have a "crew".. I'm getting too old to be on ladders 20 feet in the air hanging lasers and lights and backdrops and projector screens etc.. Since I'm the only guy who knows anything about DMX lighting, that's all my baby and I haft ado it before I even tough setting up guitar stuff.. Set up at noon, soundcheck at 5pm, rushing home, 3 hours of makeup and jewelry and stuff and hauling butt back to the club to play til 1:45am, then breaking down and unloading at the pad until 5am.. I'm getting too old for that crap..
So, I totally get ya.. I'm getting really tired, myself.. People expect me to keep doing what I do, so I can't back off the throttle production-wise.. So, its starting to not bother me at all in cancelling shows..
Friendship is like peeing your pants.. Everybody can see it, but only you can feel the warmth..