Temporomandibular Joint (TMJ) Disorder: This condition is a common cause of unilateral jaw pain, often accompanied by neck pain due to the referral of pain from the TMJ to the neck. Symptoms can include jaw clicking, locking, and difficulty chewing.

Dental Problems: Issues such as tooth abscess, impacted wisdom teeth, or periodontal disease can cause severe pain that may radiate to the neck.
Musculoskeletal Strain: Strain in the neck and jaw muscles can lead to pain in these areas, often due to poor posture, stress, or overuse.
Cervical Spondylosis: Wear and tear on the discs in the neck can cause pain that may be referred to the jaw, especially if there is nerve root compression.
Trigeminal Neuralgia: Although more commonly associated with facial pain, trigeminal neuralgia can sometimes cause pain that is perceived in the jaw and neck area.

Acute Coronary Syndrome (ACS): Although less common, jaw and neck pain can be atypical presentations of a heart attack, especially in women. It is crucial to consider ACS in the differential diagnosis, especially if accompanied by other symptoms like chest pain or shortness of breath.
Stroke or Transient Ischemic Attack (TIA): Pain in the jaw and neck can occasionally be a symptom of a stroke or TIA, particularly if there are other neurological deficits.
Infections (e.g., Parotitis, Mastoiditis): Infections in the parotid gland or mastoid process can cause severe pain in the jaw and neck area, often accompanied by fever and swelling.

Giant Cell Arteritis: This condition can cause jaw claudication (pain in the jaw when chewing) and neck pain, among other symptoms, due to inflammation of the blood vessels.
Eagle Syndrome: An elongated styloid process or calcified stylohyoid ligament can cause sharp pain in the jaw and neck, often exacerbated by swallowing.
Neoplastic Processes: Tumors in the jaw, neck, or base of the skull can cause unilateral pain in these areas, though they are less common causes of such symptoms.