Also: while reading.
And while cracking a safe.
What it all would add is a reason to consume caffeine pills and such stimulants, just to make sure there wouldn’t be a slightest chance to fall asleep inadvertently.
I know a tiredness mechanism already exists - this would just be an addition on top of it. It’s not so much about exhaustion but poor self-control, and propensity of giving in to the urge to sleep under optimal and pleasant sleeping conditions.
Also, I forgot to factor in optimal warmth.
I would want this to happen only rarely, and with fair early warning. Obviously control freaks enthusiasts wouldn’t enjoy this very much but those of us who welcome a bit of chaos and randomness… I see nothing but glorious possibilities of mayhem in this. The stories that players would tell…
I’ll try to list the factors for ease of falling asleep:
- Fullness (easier to sleep with full stomach)
- Thirst (just don’t be thirsty - minor factor)
- Warmth (not too cold, not too warm)
- Exhaustion (only while Very Tired, or with higher exhaustion, possibly Tired if all other conditions are optimal)
- Sound (can’t sleep if noisy)
- Pain (can’t sleep if in too much pain)
- Encumbrance? (prevent sleep if overburdened, or wake up if it turns into pain)