Most people with hypertension have no symptoms. That's why it is so dangerous. You can have high blood pressure for years or decades and not realize it. Only a few people will have symptoms (e.g., dizzy spells, headaches, nose bleeds) related to very high blood pressure. All too often, however, a heart attack, stroke, or other serious problem is the first sign of hypertension. The only way to know for sure is to have your blood pressure checked.