A 43-year-old car mechanic, with no prior history, comes to the Emergency Department because of...

The most likely diagnosis is organic solvent intoxication because the episodes are recurrent, acute, and specifically occur at work in a car mechanic. MCCQE objectives in occupational and environmental medicine emphasize recognizing workplace exposures that cause transient neurologic symptoms. Organic solvents (e.g., toluene, xylene, gasoline vapors, degreasers) can produce acute CNS effects such as dizziness, imbalance/ataxia, nausea, lightheadedness, and mild confusion or disorientation, often with a normal routine exam and basic labs once exposure ceases. The clear temporal relationship to the workplace and repeated similar episodes strongly supports an exposure-related cause. Lead toxicity is typically subacute/chronic, presenting with abdominal pain, constipation, neuropathy (wrist/foot drop), cognitive changes, anemia, and basophilic stippling—rather than brief episodic disequilibrium. A cerebellar tumor would cause progressive, persistent symptoms and focal neurologic findings. Ear infection–related vertigo would not reliably recur only at work and usually has ear symptoms or exam findings. Alcohol intoxication is less consistent with a repeated workplace-only pattern without corroborating signs.