Weird thought, but I don't see my pigs asleep as a rule. Only exception was GP2 who used to fall asleep on my shoulder and roll onto my lap , very judgey if I didn't catch him. I did learn to recognise the signs though and wedge my forearm round him.
He used to sleep in the run, curled like a croissant with GP1 (his brother) standing guard.
GP5 sometimes nods off in the run but she's a ruby eyed Himalayan so she might just be keeping her eyes tight shut against that nasty sunlight,
The sound of my heavy hairy trucker hands opening the Pighouse door would wake them up I reckon, or maybe they stay on duty in rotation.