If you pass out it means you aren't getting enough oxygen to your brain. It's very dangerous and can cause permanent damage. As for what it feels like, well it sux. It's embarrassing, and if you hit your head it's painful. You're unconscious so there's basically no feeling at all until you come back around with a sort of a hangover,
Moderation!!! Nitrous is not dangerous in moderation. Inhaling until you pass out is really bad though.
