I've found that those kinds of things often sound like they will be much worse than they turn out to be.
Is it one where they sort of put you under, but not really? Every time I've had one of those I wake up and ask, "Is it over?". The nurse always says something like, "Oh yes. It went great! You were talking to us the whole time!". Leaving me to hope I didn't curse at them (too much) the whole time.
But they implied that I didn't, so it couldn't really have been too bad. Hope it goes well for you.