An airline pilot friend of mine admits to nodding off in flight once, then waking up:
'Oh, sorry John, how long was I out?'
'John? JOHN!!!'
My first real job was as a computer operator on an IBM mainframe, which was shiftwork. On a nightshift week, I found that if I stayed awake though Monday and went to work Monday night, then came home on Tuesday morning and went to bed, I'd wake up Tuesday evening feeling half-dead, and moped around not doing anything for the evening, then going to work again. Rinse, repeat though the week, so by the end I'd done nothing but work, sleep, and feel too lousy to do anything, so I'd effectively lost a week of my life.
So I decided to stay up. I'd usually make it to Wednesday morning OK (no sleep for about 48hrs) but sometimes the drive home was 'interesting'. I could have the radio up loud, the window open, my head out in the breeze, and I still couldn't stay awake - even holding one eye open with my fingers wouldn't work! When this happened I'd pull into a layby and get half an hour's kip, which was enough that I could then drive home.
I was young and stupid, and I certainly wouldn't do it now, but it taught me that if you're really tired, *nothing* will keep you awake. In the context of this place, 'we' really need to accept this and tackle it as a problem, and making it the pilots' responsibility to stay awake won't (doesn't) work. Like spotting your own errors, it's not effective, so someone/something needs to do it.
Perhaps some sort of challenge/response that needs to be handled every now and then when the crew haven't made any inputs to anything for a while, and a wake up call if they don't respond?
Oh, and it would be a good idea in road vehicles, too!