Getting put under sleep?

So I’m rlly confused i have to have teeth out and they said i could get put under sleep where i can get injected in my vein or have gas to knock me out but if i have the gas is that just a way of knocking me out before they inject me? surely gas can’t knock me out for that long... if i chose the gas when i wake up... show more So I’m rlly confused i have to have teeth out and they said i could get put under sleep where i can get injected in my vein or have gas to knock me out but if i have the gas is that just a way of knocking me out before they inject me? surely gas can’t knock me out for that long... if i chose the gas when i wake up will there be a needle in my hand???
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