it sounds like your atypical symptoms (neurological) are a result of a generally poor health due to long-standing GERD, rather than directly caused by GERD.
It also sounds like you always ate anything you wanted (including those "forbidden" food) after the operation. There is a very strict dieting code to follow for those who took Nissen in order to promote recovery and to maintain the recovery. I think very likely, the eating habit is what that landed you in this place.
To reverse the damage, it will take a proper diet and a good doctor once again.
Well I must admit that I didn't restrict anything other than dairy for the most part (cooked with cheese occasionally) and completely avoided citrus after my operation.
I was just wondering if it is possible that based on my other neurological symptoms (all over muscle weakness, twitching, dizziness, etc.) that something neurological is causing my LES to not function properly. I don't even know if that makes sense it was just a thought.