So sorry you're experiencing problems. I hope your doctor can shed some light on what is going on with you. Try not to worry about the redo aspect. If a redo is the best solution to your problem, you would join many others who have gone through that. I read somewhere that about 7% of Nissen patients require a redo. While it's not fun being in that group, you're not alone.
I had the surgery in February 2009, mainly because my lungs were being killed by reflux, I coughed so much during the recovery that I suspect I began the process of undoing a stitch. After another lung issue last December, I began getting a sour taste in my mouth. I had a barium swallow that didn't show anything really, and since my lungs were managing just fine, I just lived with it.
In August I started getting lung symptoms again (not severe at all, but concerning). I decided I was going to be assertive about getting to the bottom of the reasons, since before my surgery, I let things get out of control until it was too late, and my lung problem sabotaged the chance of success.
I will gladly get a redo (if my testing deems it necessary) to prevent the problems I had prior to my first surgery. I will, though, thoroughly research the surgeons in the area to make sure they're qualified, experienced, and have many successful redos in their history. Redos are trickier, so it's even more important to have a highly skilled surgeon on the job.
Good luck with your search for answers!
Let us know what happens!