Endocrine problems, such as an underactive thyroid (called hypothyroidism), overactive thyroid (called hyperthyroidism), adrenal insufficiency (called Addison's disease), low blood sugar levels, and in some cases, diabetes, may lead to hypotension and
hence lightheadedness and
an off balance feeling.
Certain types of epilepsies and
seizures too can cause similar symptoms. If you have an accompanying headache then you must also look at benign intracranial hypertension.