Muscle Strain: The most likely cause of lateral neck pain in a drag racer is a muscle strain, particularly in the sternocleidomastoid or trapezius muscles, due to the high-speed, high-acceleration environment of drag racing, which can lead to sudden and forceful movements of the neck.

Whiplash Injury: Given the context of drag racing, whiplash injury is a plausible diagnosis. The rapid acceleration and deceleration can cause the head to whip back and forth, leading to strain on the neck muscles and ligaments.
Cervical Facet Joint Pain: The repetitive stress and strain from the high-speed activity could also lead to cervical facet joint pain, a common cause of neck pain, especially on one side.
Herniated Cervical Disc: The physical demands of drag racing might exacerbate or cause a herniated cervical disc, which could compress nerves and cause lateral neck pain.

Carotid Artery Dissection: Although less likely, carotid artery dissection is a critical diagnosis not to miss. The forceful neck movements during drag racing could potentially lead to a dissection, which is a medical emergency due to the risk of stroke.
Vertebral Artery Dissection: Similar to carotid artery dissection, vertebral artery dissection is another emergency that could be precipitated by the neck movements associated with drag racing, leading to potential posterior circulation stroke.

Spinal Fracture: While rare, the high-impact nature of drag racing accidents could potentially lead to spinal fractures, which would require immediate medical attention.
Osteonecrosis of the Cervical Vertebrae: This is a rare condition but could be considered in the context of repetitive trauma or stress to the cervical spine from drag racing activities.