Benign Paroxysmal Positional Vertigo (BPPV): This condition is characterized by brief, episodic vertigo triggered by specific head movements. It's a common cause of balance issues and can present with a normal neurologic exam, making it the most likely diagnosis given the scenario.

Vestibular Neuritis: An inflammation of the vestibular nerve, which can cause sudden onset of vertigo, balance problems, and nausea. The neuro exam might be unremarkable if the inflammation is localized and doesn't affect other cranial nerves.
Labyrinthitis: Inflammation of the inner ear's labyrinth, which can cause vertigo, hearing loss, and balance issues. Like vestibular neuritis, it might not have significant findings on a neuro exam if the condition is in its early stages.
Orthostatic Hypotension: A condition where blood pressure drops upon standing, leading to dizziness or lightheadedness. It can cause balance issues without specific neurologic deficits on exam.

Posterior Circulation Stroke: Although less common, a stroke in the posterior circulation (including the cerebellum and brainstem) can present with isolated vertigo or balance issues without other focal neurologic signs, especially in the early stages. Missing this diagnosis could be catastrophic.
Multiple Sclerosis: While less likely, multiple sclerosis can present with almost any neurologic symptom, including balance issues. An unremarkable exam does not rule out this condition, as lesions might not be in areas that cause obvious deficits on a standard neuro exam.
Vitamin B12 Deficiency: Can cause a range of neurologic symptoms, including balance issues, due to its role in the nervous system. It's crucial not to miss this diagnosis as it's treatable and can prevent long-term neurological damage.

Acoustic Neuroma: A benign tumor on the nerve connecting the inner ear to the brain, which can cause balance issues, hearing loss, and tinnitus. It's rare but should be considered in the differential for persistent or worsening symptoms.
Chiari Malformation: A structural defect in the cerebellum that controls balance, which can cause a range of symptoms including balance issues, especially with certain head movements. It's less common and might not always have a clear presentation on a neuro exam.
Superior Canal Dehiscence: A rare condition where there's an abnormal opening in the bone overlying the superior canal of the inner ear, leading to vertigo and balance issues triggered by sound or pressure changes. It's a rare cause but should be considered in patients with sound-induced vertigo.