Some people worry before surgery, others don't. That being said, I have had many operations/procedures which required general anesthesia or an epidural anesthetic (10 at last count). I get nervous before each - I think for me its because I am completely giving up control of the situation and putting myself in the surgeon and anesthesiologist's hands. And that's tough for me because I'm a control freak.
So, it's ok to worry. But know that the likelihood of a surgical mishap is incredibly small. There is a calculator put together by one of the surgeon's groups using all kinds of statistics. Put in your surgery - I made some assumptions - that you were under 65, and had a BMI over 35 (therefore qualifying for a sleeve) and it came up with a 0.1% chance of death due to surgery.
So, by that calculation - it's more dangerous to cross the street. Be careful going to your car! Or flying home. It's ok to have anxiety. It will be fine.