Hi KJ,
For a beginner you sure have lots of reactions which means that zhineng qigong that you have got it right from the very beginning. I should think that it could be due to your taiji practice that you experience such immediate effects.
It is hard to tell why it is localised in your neck area. Rest assured that you are progressing well and you should keep doing whatever you are doing now.
More amazing things to come when you practice long enough.

Hun yuan ling tong!
Kian Tee