Yesterday I dove Frc to around 10 m. On one dive I was focused on 1) keeping a shut glottis 2) relaxing upper body ensuring there is no tension. I'm taking a mouthfill at 1- 2 m and descending head up after a pull with hands to sink. Focusing on the two mentioned factors I forgot to let my nose open to blow some air into the mask. Once at the bottom I used the usual frenzel tongue pressuring maneuver to try and blow some air into the mask. It was quite hard. Tried harder and it is at that point that I felt something odd in neck area like pain or pressure. At start it felt like a vain popping left of trachea trying to feel with my hand what's wrong. In mirror I can't notice something obvious but today I tried exact same dive and did feel the pain in the same area. Tried the exact same dive full lung and It was perfect. I think its not some type of barotrauma since trachea feels fine but some nerve getting injured but why does it only appear in diving ?