Yes, it happens frequently. You wouldn't actually be asleep but it would have the same effect.
Try not to!
Anything displacing oxygen or lowering oxygen will cause fainting / losing consciousness / sleepyness even death if (asphyxiation).
Best way is not to use that, Trained doctors know how to put patient a sleep for surgery etc.
Yes, but that'd involve a concentration of the gas that is very toxic. It could, in fact, kill you. And the person administering the gas would go to prison for murder.
Yes. If your dad laughs and farts, you are receiving laughing gas while falling asleep
I sure hope so, I'm having dental implants put in soon.
Yes. I normally get sleepy when they are starting it.