Welcome to the forum but sorry to hear your pain.
As Jo said it is most frequent that the EMG may not show some nerve damage until it affects the larger nerves that move the muscles. The smaller sensory nerves are the first affected These are the ones that feel heat of a candle, relay pain messages, the EMG is testing the larger nerves that make the muscles move...tell the arm to push pull lift etc.

However, it sounds like you may have some short bands of the neck that support the head. half of society has this anomolie, but for an injury or assault there may never be an issues. With short bands, nerves inflamed, then working them out can be a dynamic.
Falls, whiplash, repetitive strain, overuse syndromes.

With your muscle building the nerves being inflamed cause the muscle to splint around the nerve to protect it. As the muscles are spasm;s you are working them making the nerve very unhappy.

The nerves insert into the muscle; vicious circle.
Maybe if the person doing the test has you replicate the positions you are in when the pain is there may help.
Good luck tomorrow