Hypertension (high blood pressure) leads to heart attacks, strokes and aneurysms. The person suffering these things can not "feel" the high blood pressure causing them - it is painless and therefore "silent".
Carbon Monoxide increases blood pressure when it is breathed in it sticks to the blood cells, meaning oxygen cant stick to it. This then leads to less oxygen being transported round the body, leading to high blood pressure.
To make sure you have good blood pressure and to determine whether you have high blood pressure. 120/80 is ideal. If your blood pressure is high you may need medication. A low blood pressure means the blood volume in the body is low. Low blood pressure is as dangerous as high blood pressure.