For months I was the calm, organised one. Spreadsheets, questions lists, the lot. Now the dates are fixed and flights are booked and suddenly I'm lying awake going "why am I doing this, what if I hate it, what if I'm being vain". Nothing has changed except that it's real now.
Did other people go through this? How did you tell the difference between normal nerves and an actual "I shouldn't do this" feeling?
Very normal. The way I'd separate them: nerves are usually about the unknown (pain, recovery, what if). A real "no" tends to be about the reason itself, like you're doing it for someone else, or the thing that bothered you doesn't actually bother you anymore. If your reasons still hold up on a calm day, it's probably nerves. And it's fine to have questions you want to go over with the surgeon again before the day. Asking more questions isn't backing out.
the "what if I'm being vain" voice is so loud at 2am and so quiet at 2pm. try to only make decisions at 2pm