Your symptoms sounds awful and must be hard to live with.
Your gf 'advice' is worse than unhelpful as what's she's saying is probably making you think that it's something you should go on living with and that have the procedure isn't really necessary, when clearly it is.
Of course you'll wake up. You'll know nothing about what's happening to you and then you'll be awake and it'll be over.
I've had many, many operations, the vast majority have been gynecological and I've obviously woken up after every one.
The anesthetist is incredibly skillful and your procedure is very routine. Of course you're going to feel nervous and fearful, especially if you've never been through anything like this before but you need to get to the bottom of this and start getting yourself treated. This is the first step to that.
Just think, all this worry, but tomorrow night you'll be at home again. If you put it off now, the chances are your symptoms will just get worse, as clearly they're not going to go away on their own, and you will probably be going through the same worry a year or so down the line.
Don't cancel, you'll be doing yourself no favours.