Diabetes lowers blood pressure because excess sugar causes increased urine output and fluid loss. Adrenal insufficiency and both hypo and hyperthyroid conditions can result in hypotension. Heart disease can lead to chronic low blood pressure or more severe orthostatic hypotension -- low pressure and dizziness on standing. Conditions resulting in dehydration including diarrhea and vomiting can produce this effect, as can folic acid deficiency, anemia, blood loss, and internal bleeding.

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