Benign Paroxysmal Positional Vertigo (BPPV): This condition is characterized by brief, episodic vertigo triggered by specific head movements, which could explain the postural dizziness and gait instability. However, it less commonly presents with hearing changes or tachycardia, making it a less perfect fit for all symptoms described.

Meniere's Disease: A disorder of the inner ear that affects balance and hearing, leading to episodes of vertigo, tinnitus, hearing loss, and a feeling of fullness in the ear. The combination of hearing changes, dizziness, and potential nausea aligns well with this diagnosis.
Vestibular Migraine: Characterized by episodic vertigo, often accompanied by headache, sensitivity to light and sound, and sometimes nausea and vomiting. While hearing changes are not a primary symptom, the broad range of neurological symptoms can sometimes include tinnitus or sound sensitivity.
Labyrinthitis: An inner ear disorder that can cause dizziness, loss of balance, and hearing loss. The inflammation of the labyrinth could explain the combination of vertigo, hearing changes, and nausea.

Stroke or Transient Ischemic Attack (TIA): Although less common, vertebrobasilar insufficiency can present with vertigo, nausea, and gait instability. Hearing changes and tachycardia could be associated with the stress response or specific areas of the brain affected. Missing a stroke or TIA could be catastrophic.
Multiple Sclerosis: An autoimmune disease that affects the brain and spinal cord, potentially causing a wide range of neurological symptoms, including vertigo, gait problems, and sensory changes. While not all symptoms perfectly align, the unpredictability of MS makes it a "do not miss" diagnosis.
Cardiac Arrhythmias: Certain arrhythmias can cause dizziness, nausea, and tachycardia due to inadequate cardiac output. Although hearing changes are not typically associated, the potential for a life-threatening condition warrants consideration.

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 it's a possible explanation for some of the symptoms, its rarity and the fact that it typically presents with more gradual onset make it less likely.
Autoimmune Inner Ear Disease: A rare condition where the immune system attacks the inner ear, leading to hearing loss and vertigo. The presence of tachycardia and nausea could be part of a broader autoimmune response, but this diagnosis is uncommon and would require specific testing for confirmation.