There's no need to be terrified! The surgery and colonoscopy won't be fun, but they also won't be nearly as bad as you think. :D
Doctors do tend to significantly underestimate recovery time. I doubt very much that you will be back to work in a few days - more like two weeks. You won't be in a lot of pain those two weeks, but you won't be very comfortable either and two weeks is really much better for taking care of yourself and making sure that your recovery goes well. You will also want to keep the butt clean and soak in the bath quite a bit too, and it's hard to do those things at work! A lot depends on what you do, though. A desk job might be uncomfortable if you go back to work before two weeks are up, but I'd say manaul labour and heavy lifting are out of the question.
The colonoscopy won't be so bad. I had one in Feb. The worst part is drinking down that awful liquid they give you to make you go. It tastes terrible, but here's a very good trick: put it on ice and make it very cold before you drink it and it won't taste bad at all. It makes you go like you wouldn't believe, but it's surprisingly not very painful. I had a colonoscopy when I had my fissure and I was surprised that it didn't really hurt when I had poop blasting out of me at velocities approaching the speed of light!
it was more alarming than anything else. I really didn't think it was humanly possible to poop like that!
It's a good thing that your doc wants to be thorough and test you for IBD. That's scary, I know. That's why I had my colonoscopy too. You doc is likely testing you for Ulcerative Colitis and Crohns Disease (two forms of IBD). Fistulas and fissures are sometimes caused by IBD, usually Crohns. Do you have digestive problems? IBD usually comes with abdominal cramps, bloating, diarrhea and other symptoms (very rarely, Crohns is confined to the anal area, like in the case of one boardie here, so it is good that your doc is checking you out). But unless you've got other symptoms, then I don't think you need to be too worried about IBD at this point.
A few boardies here have had their fissures try to heal, but form fistulas instead, so that may very well be what happened in your case. If that's so, then it's pretty easy to fix and you will be fine! I'm sorry you're facing a rough few days, but we are here to support you. There will be an end to this - hang in there!