With any imbalanced posture (postural distortion pattern), including text neck posture, asymmetrical pathomechanical forces are placed into the tissues of the body. These forces have to have an effect. I believe it is impossible to argue that pathomechanics do not lead to dysfunction.
A tension headache is caused by excessive pulling force of tight muscles in the back of the neck that exert tension on their attachments on the head.
Muscle spasming of the neck occurs because of its role in neck movement and posture, as well as it role in upper extremity movement and posture.