Presyncope, more commonly known as lightheadedness, can be caused by many different things, including: Addison's disease (adrenal insufficiency) Cardiac arrhythmia (heart rhythm disorders) Dysautonomia (nervous system malfunction) Heart valve disease Hypoglycemia (low blood sugar) Hyponatremia (low blood sodium) Hypernatremia (high blood sodium) Medication side effects Pulmonary hypertension Straining (like extreme coughing) Seizures