What is the most likely reason for a patient to present with nystagmus and dizziness with sudden onset?

The presence of nystagmus and dizziness with sudden onset is most consistent with vestibular neuritis. This condition is characterized by inflammation of the vestibular nerve, which plays a critical role in maintaining balance and spatial orientation. The sudden onset of symptoms, including vertigo and abnormal eye movements such as nystagmus, often results from a viral infection that affects the vestibular system. Patients typically report a sudden episode of intense spinning sensation (vertigo), which can be quite debilitating.

In contrast, labyrinthitis, which also involves both cochlear and vestibular systems, tends to present with additional auditory symptoms, such as hearing loss or tinnitus, due to its impact on the inner ear structures. Benign positional vertigo usually causes episodes of vertigo triggered by changes in head position but is not characterized by the same acute onset of persistent symptoms seen in vestibular neuritis. Meniere's disease involves recurrent episodes of vertigo, hearing loss, tinnitus, and aural fullness, but episodes tend to develop over time rather than occurring suddenly. Therefore, the most likely reason for the presentation of nystagmus and dizziness with sudden onset is indeed vestibular neuritis.