Vestibular Neuritis or Labyrinthitis: This condition often presents with sudden onset of vertigo, hearing loss, and tinnitus, usually in one ear. The associated lightheadedness and bradycardia could be secondary to the vestibular system's influence on balance and autonomic functions.

Meniere's Disease: Characterized by episodes of vertigo, tinnitus, hearing loss, and aural fullness, typically affecting one ear. Bradycardia and lightheadedness could occur during acute episodes due to autonomic nervous system responses.
Acoustic Neuroma: A benign tumor on the nerve connecting the inner ear to the brain, which can cause hearing loss, tinnitus, and balance problems. While less common, it could potentially lead to symptoms like lightheadedness and bradycardia, especially if it compresses nearby structures.
Inner Ear Infection: Infections like otitis media or interna can cause hearing loss, vertigo, and potentially affect heart rate variability, leading to bradycardia and lightheadedness.

Stroke or Transient Ischemic Attack (TIA): Although less common, a stroke or TIA in the posterior circulation can cause sudden hearing loss, vertigo, and autonomic dysfunction leading to bradycardia and lightheadedness. Missing this diagnosis could be catastrophic.
Multiple Sclerosis: An episode of multiple sclerosis could present with a wide range of neurological symptoms, including hearing loss, vertigo, and autonomic dysfunction. Early diagnosis is crucial for management.
Cardiac Arrhythmias: Certain arrhythmias, particularly those involving the sinoatrial node, can cause bradycardia and symptoms of lightheadedness. If associated with hearing loss, it might suggest a more complex syndrome or an embolic event affecting the ear.

Superior Semicircular Canal Dehiscence: A rare condition where there's an abnormal opening in the bone overlying the superior semicircular canal, leading to hearing and balance symptoms. It could potentially cause autonomic symptoms like bradycardia.
Cogan Syndrome: A rare disorder characterized by recurrent corneal inflammation and vestibular-auditory symptoms, which could include hearing loss, vertigo, and potentially autonomic dysfunction.
Sjögren's Syndrome: An autoimmune disorder that can affect exocrine glands and potentially cause neurological symptoms, including hearing loss and balance issues, though bradycardia would be less common.