HYPERtension is high blood pressure. Did you mean to say you have HYPOtension? The only thing I've seen mentioned about fainting and low blood pressure is a situation where a person with low blood pressure has been sitting/squatting for a long period of time and suddenly stands. You can lessen the possiblility of fainting by getting up and stretching or walking every few minutes if you're going to be seated for a while. Also, rising slowly and giving your body a chance to adjust to the new bloodflow will help.
Standing causes a sudden drop in blood pressure because the blood goes to the lower extremities. This happens for all people. In those with normal or high BP, the body sends a signal for the heart to pump faster... to compensate for the change in blood flow. For people with low BP, the body doesn't send this signal and fainting can occur.