If your blood pressure has been very good for most of your life and then suddenly rises to a dangerous level, could there be an infection or some other medical condition that caused the sudden jump?
A temporary rise in your blood pressure probably shouldn't generate much concern, but a sudden and dramatic rise in blood pressure that continues for more than several days or weeks usually requires careful medical attention.
Your blood pressure is constantly changing, depending on your activity, your position, your mental state, and even the time of day (blood pressure is lowest during deep sleep, but often peaks during the early morning hours). Two blood pressure measurements taken even minutes apart may be different by 20 points or more, especially if you relax, or exercise, or drink a cup of coffee or smoke a cigarette.
That said, a series of blood pressure measurements taken at the same time of day, while you are seated and relaxed, should cluster in the same 10- to 20-point bracket. Your systolic blood pressure — the "top" number — may vary more than your diastolic or "bottom" blood pressure reading.
If you or your doctor note a single high blood pressure reading, it usually makes sense to simply repeat a second or third reading before becoming concerned. Often the blood pressure will return to normal, especially if you are given a chance to relax. If the immediate follow-up readings don't improve, your doctor may still recommend a series of readings taken over several days before recommending treatment. It's important to realize that anything short of very high readings — for example, greater than 220/110 — is unlikely to cause damage in the short term. In fact, using powerful drugs that lower blood pressure too quickly can often cause more harm than good.
What if your blood pressure has always been normal, but then rises over a short period and stays elevated? This can signal an important medical cause for your high blood pressure, including:
Side effects from certain drugs (both prescription and "street" drugs such as cocaine and amphetamines)
Conditions where the body produces too much of certain hormones
Narrowing of the blood flow to the kidneys, or other types of kidney disease
Certain complications of pregnancy
Under these circumstances, your doctor will often begin a medical evaluation to find a cause for your elevated blood pressure at the same time that treatment is begun.