Welcome to the Healing Well GERD forum! You're definitely in the right place. Joy have given you the basic experience in the hospital. It's surprisingly easy, and while you can expect some post-surgical pain, you'll be surprised how quickly your outsides heal.
That, however, can be deceiving. It seems that we heal so quickly on the outside, we sometimes forget that our insides were scrambled up with an egg beater, then stretched and stitched. There have been major changes made to our upper GI tracts, and those changes are going to require months to heal.
Hopefully you've found a surgeon who had done many, many Nissen surgeries. The experience of the surgeon is critical to creating a positive outcome.
Have you discussed the post-op diet that your surgeon intends to put you on? It would be helpful to know what his protocol entails. Some are on liquids for a long time, but mine allowed me to use my own good judgement and eat anything that could be chewed to a liquid, which gave me a lot of leeway. I never had any problems with this eating protocol, but I was extremely careful to take very small bites and chew, chew, chew.
You'll want to stay away from bread (although if you toast that bread it chews to a liquid), sandwiches, and steak for about 8 weeks).
As Joy said, you'll only need the narcotic pain meds for a short time. Be sure to buy some liquid Motrin or Tylenol to have on hand for the early days/weeks.
Again, welcome to the group! If you have any specific questions, we'll do our best to answer them. When you post after your surgery, we'll be here to welcome you to our Wrapped Club!