I have never had any worries regarding the distance or duration of my flight to Thailand or me going and staying there all alone, and I have never feared the surgery itself or the possibility of complications or the pain and chores of the recovery period.
But the months leading up to my SRS date were full of ever worsening anxiety that something in that delicate chain of events could go wrong and derail everything completely. I was worried that my flight could be cancelled, so I booked an additional backup flight with another airline months in advance (and then my flight actually WAS cancelled two days before the due date). My referral letter obviously was very important, and I must have checked a hundred times whether it was still there while I was travelling. I knew I had stones in my gall bladder, and I could only hope that they would not act up at the worst possible moment. Two days before the surgery I almost fainted during breakfast, but I told nobody, fearing the surgery could be postponed or cancelled (they checked my heart rate and blood pressure anyway at least four times the morning before the operation, and everything was alright).
In the end, things turned out well and I managed to have my SRS, but more than anything else I was relieved when I woke up that nothing on earth could come between us anymore.
Prepare well, be careful, and you will be fine.