Speaking for myself of course, hope this helps.
1. what exactly does the pain feel like right after surgery?
Most of my pain was on my incisions themselves. And I wouldn't call it pain really. It was more like a tightness. Same as with any large cut. I had no internal pain at all. My larger incision was tacked down to my abdominal wall so when ever I tried to sit up or move the wrong way it would pull. But it was more annoying than anything. That eventually released and after that I didn't feel any more pain what so ever. Of course everyone has different pain tolerances, mine happens to be pretty high.
2. Do they let you wear underwear during surgery?
I was completely nude under my gown. I was extremely worried about this too. I was insecure about having so many people around me while I was completely naked. But once you put your gown on they gave me blankets that I covered up with the entire time I was awake. To answer you question, No. They told me to take them off.
3. were you have to use the restroom by yourself?
I tried to go by myself about 4 hours after my surgery. Bad ideal lol. I made a mess. I recommend a spouse or family member to be there to help you the first time if you are not sure of yourself. I wish I wouldn't have been stubborn lol.
4. Is there a trick to making it less painful when getting up or sitting?
I found there was only two ways that I would not be able to feel any discomfort. One was to left my wife pull me up from the couch/recliner and or I would basically roll off the couch and lift myself with my legs and back. After a few days I could gradually get up with no to little pain though. If you take your meds like you should then I don't think the pain is going to be that severe that you will not be able to get up at all.