What you're experiencing is not at all our of the realm of the "normal" at eight days post-Nissen. Your wrap is still swollen and actually becoming more swollen by the day. This is to be expected. (Remember that peak swelling is on or about Day 14.) As long as liquids are going down, you can get some nutrition and fluids. It is true that water tends to sit at the wrap site and kind of dribble down during the early days. Just sip liquids and take small amounts at a time. Be sure to stay away from iced drinks and straws.
Don't panic. It's not always going to be like it is now. You've had major surgery, and your upper GI tract has had a major revision. If you can find a way to relax into your recovery, rather than fight against it and be fearful, you'll do better. I know it's hard not to worry that the way you feel now is the way you'll always feel, but that's not true.
Did you ever read through my first 19 days journal?
It might help you understand better what you might expect in the next week.
Unfortunately surgeons don't really prepare patients well for the recovery...I don't know if they don't want to scare them, or just don't really know what they will experience.
The constipation is very common...some have diarrhea, some constipation. The pain meds slow down the intestine and make it more likely to become constipated. Also you're eating so little that there's no need for them to move. Your body hasn't adjusted to your reduced food intake.
Day 8 is the very, very, very beginning of healing. The majority of the healing takes six months, while the remaining takes an entire year. I experienced additional improvement into the second year.
I agree with bowecho, that additional pain meds to get you through this rough spot would be helpful. I really don't think you need to be scared. The first two weeks are rough, and with the increased swelling, swallowing can become very difficult. Once the swelling has run its course, it will begin to recede, and your swallowing will improve.
Relax, and trust that your body will adjust, and that healing will occur.
Take a deep breath. Think positive thoughts.
We're here for you!