While you may have controlled your hypertension for some time, it doesn't follow that other changes have taken place that are typically associated with aging. You may have heart failure, as an example, or a blockage of an important artery, or mitral valve or aortal valve prolapse or failure....all quite aside from your medically controlled hypertension. These things can cause low blood pressure as they impair cardiac function. Impaired cardiac function can lead to blackouts and syncope. You must relay these events to your cardiologist or internist.