depends on what they do really and how well you tolerate pain. if they are just scraping out all the bad junk. you will have pain like a bad sinus headache, it feels a bit different. you will also feel a little stuffed up for a few days due to swelling and packing.
if the surgery is more invasive such as they have to cut things out, cut out scar tissue or even bone to make windows and the openings in your sinuses wider. that will cause more pain. it will vary depending on how much they remove but it can be pretty painful. the good news is the most painful part of it you will be to out of it to notice to much, other good news they will give you good pain medication to help manage it...and it shouldnt last more than a few days.
for me I tolerate pain really well. so all of my 6 or 7 (i lost count) sinus surgeries they havent been to painful. i have had them widen openings, remove scarred and diseased tissue and just remove bad gunk...the easiest is of course with they just remove gunk, the hardest was when they had to widen openings and remove diseased tissue. when i say hardest it took me a bit longer to recover. like the easiest ones i was back to normal in 2-3 days the hardest ones i was back to normal in about a week. i rarely had to take any pain medication with the hardest ones except for the first day or two, in an odd occasion i had to take them for about 4 days, but it was like one pill did the job for me for the whole day, i usually took them at night so i could sleep plus pain pills make me sleepy. usually just tylenol worked good for my pain.
again pain depends on what they do during surgery and how well you tolerate pain. if you cant tolerate pain at all even the simplest of sinus surgery will hurt alot. if you can tolerate pain really well you wont have much pain at all with the simplest type of sinus surgery. it also depends on how they manage your pain as well.
some tips that will help you though is take it real easy for the next three days after surgery. even if you feel fine. take off work or school even. no heavy lifting, try not to stay bent over for to long, infact try to avoid it. even if you feel fine. ice packs feel good. but key here is just relax for a few days. it helps the healing process and if you over do it to soon you may wind up with more pain and just feeling icky. the anasthetics alone take alot out of a persons body so you just need to relax.
