I had a lengthy back op as my first general anaesthetic!
Best sleep I ever had..
The funny thing was, I woke up refreshed, lying on my back and my first thought was "Bugger, if I'm on my back they can't have done the op, because surely they wouldn't have my body weight on the surgery site".. I asked the nurse who said "No, everything went well, we got it done in 4 hours and no complications" It took me a while to accept that, I just had this amazing feeling of serenity (morphine induced!)
But, obviously slightly nervous going in to theatre, however, the count down from 10, I think I made it to 7, that was it..
Ironically I now work in the medical device industry and work with clinicians all the time, primarily for cardio thoracic therapies and life support, so lots of anaesthesia, from general to cardioplegia and certainly have much less worries about surgery.. considering our stuff is used when you are in the most dire of conditions, the outcomes are ridiculously positive..
Try to relax! We can't stop your mind going in circles, but can reassure you that it's a positive experience and obviously focus on the fact you'll not be in any more pain!