Hi, thanks for writing to HCM.
From your description, it seems to me that your imbalance is due to a problem in your "inner ear" called as MENIERE'S DISEASE.
Some of the symptoms include balance disturbance, lightheadedness
headache,vague feeling of uneasiness etc. The exact cause of this disease is unknown. In some people there have been found certain "triggers" which can set off these attacks.
These triggers include stress
, overwork, fatigue
,too much salt in the diet, emotional stress etc . In your case driving for 200km could be attributed to stress and overwork.
I suggest you to consult a "Otorhinolaryngologist" (ENT surgeon) for evaluation and treatment. Hope this helps