Musculoskeletal strain: This is the most common cause of neck pain, often resulting from poor posture, overuse, or acute injury. The stable vitals support a non-life-threatening condition, making musculoskeletal strain a plausible first consideration.

Cervical spondylosis: A common condition characterized by wear and tear on the discs in the neck, which can cause pain and stiffness. It's more likely in older adults but can occur in any age group.
Herniated cervical disc: This condition occurs when the soft inner gel of the disc leaks out through a tear or crack in the outer layer, potentially irritating nearby nerves and causing pain.
Tension headache: Often involves the neck and can refer pain to the head, making it a consideration for neck pain, especially if there's a history of stress or tension.

Subarachnoid hemorrhage: Although less likely with stable vitals, a sudden, severe headache (often described as "the worst headache of my life") can sometimes be accompanied by neck pain. Missing this diagnosis could be fatal.
Meningitis: Inflammation of the protective membranes covering the brain and spinal cord, which can present with neck stiffness and pain, along with fever and headache. Early diagnosis is crucial.
Cervical spine fracture: Even with stable vitals, a fracture could be present, especially if there was trauma. This is a critical diagnosis not to miss due to the potential for spinal cord injury.
Epidural abscess: A collection of pus in the epidural space that can compress the spinal cord, leading to severe consequences if not promptly treated.

Multiple myeloma: A type of blood cancer that can cause bone pain, including in the neck, due to bone lesions.
Cervical spine infection (e.g., osteomyelitis, discitis): Infections of the cervical spine are rare but can cause significant pain and have serious consequences if not treated.
Referred pain from thoracic or abdominal pathology: Rarely, neck pain can be referred from conditions affecting organs in the thorax or abdomen, such as pancreatic cancer or a thoracic aortic dissection.
Neck pain due to systemic diseases (e.g., rheumatoid arthritis, lupus): Certain systemic diseases can cause neck pain, though this would typically be accompanied by other symptoms.