• Sleep can function as mental bondage. If you're asleep and can't be easily woken, you're completely helpless and vulnerable. If you're sufficiently drowsy and out of it, you're still basically helpless, but with the added bonus of potentially being somewhat aware of what's happening.
• The many ways to be forced to sleep -- surgical drugs, chloroform rags, hypnosis, sleeping spells and potions, tranquilizer darts, hidden sedatives in food or drink...
• The onset of sleep can be quick, barely giving you time to react before you're out, or so gradual you won't even realize what's happening until it's too late (and everything in-between).
• Uncertainty -- being put to sleep against your will, not knowing what will happen to you while you're defenseless. Being carried away as you fall asleep, not knowing where you'll be when you wake.
• The fight to stay awake, because it feels like something you should be able to fight, to overcome with enough willpower, but...
• The inevitability of being put to sleep. You might not feel the effects of the drugs or magic right now, you might feel wide awake, but sleep will be coming for you.
• Heavy eyelids fluttering and straining to stay open, drooping and closing all by themselves.
• Confusion and disorientation as the drowsiness sets in.
• Floating in and out of consciousness, perhaps just able to hear people discuss you or feel them handling you.
• Deep hypnotic sleep where your conscious mind is shut down and your subconscious is utterly vulnerable to suggestion.
• Glassy, dazed eyes with nothing behind them -- your eyes might still be open, but you're still fast asleep.
• Sleepwalking, wandering around in a trance, unaware of your surroundings -- or perhaps your sleeping mind is following someone else's commands...
• Memory gaps and not knowing what happened while you were sleeping.
