Benign Paroxysmal Positional Vertigo (BPPV): This condition is characterized by brief, intense episodes of vertigo triggered by specific head movements. It is the most common cause of vertigo and has a sudden onset, making it the single most likely diagnosis.

Vestibular Neuritis: An inner ear disorder that causes inflammation of the vestibular nerve, leading to severe vertigo. It often follows a viral infection and can have a sudden onset.
Labyrinthitis: Inflammation of the inner ear's labyrinth, which can cause vertigo, hearing loss, and tinnitus. Its onset can be sudden and is often related to viral or bacterial infections.
Meniere's Disease: A disorder of the inner ear that causes episodes of vertigo, tinnitus, hearing loss, and ear fullness. While its onset can be sudden, it typically involves a combination of these symptoms.

Posterior Circulation Stroke: Although less common, a stroke affecting the posterior circulation can cause sudden onset vertigo. It is critical to rule out this condition due to its severe implications and the need for immediate treatment.
Vertebrobasilar Insufficiency: A condition where the blood flow through the posterior circulation of the brain is compromised, leading to symptoms that can include sudden vertigo. Early diagnosis is crucial to prevent a full-blown stroke.

Multiple Sclerosis: An autoimmune disease that can affect various parts of the brain and spinal cord, including areas responsible for balance, leading to vertigo. However, vertigo as a sole presenting symptom is rare.
Acoustic Neuroma: A benign tumor on the nerve connecting the inner ear to the brain, which can cause vertigo among other symptoms like hearing loss and tinnitus. Its onset is typically gradual rather than sudden.
Perilymphatic Fistula: An abnormal connection between the inner and middle ear, causing fluid to leak and leading to vertigo, hearing loss, and other symptoms. It is a rare condition that might follow head trauma, surgery, or barotrauma.