Many Americans who recently went to bed thinking they had normal blood pressure woke up with hypertension. That wasn’t the aftereffect of a nightmare. Blood pressure guidelines have changed.

A revamping of guidelines by the American Heart Association and the American College of Cardiology now defines high blood pressure as 130 over 80 or greater for anyone with a higher risk of heart attack or stroke, in addition to those ages 65 and older. Those at higher risk include individuals with diabetes, heart disease or kidney disease.

That’s a big bump from the previous 140 over 90. This means an estimated 103 million Americans have hypertension, up from 72 million under the old guidelines.

So why the change?

Recent studies indicate the risk of heart attack, stroke and death is significantly reduced with blood pressure that is far lower than what had previously been considered normal. The result is that many of us will now have to take steps to reduce our blood pressure. That may mean a regimen of exercise and a change in diet.

Others will require medication. According to one estimate, 4.2 million more Americans will now be candidates for drug therapy.

The New York Times reports that nearly half of adults, and about 80 percent of those age 65 or older, will have to take steps to reduce their blood pressure.

But the news isn’t all bad. The guidelines also note that healthy people with a low risk of heart attack and stroke can stick to the 140-over-90 standard.

It may have been a rough wake-up call to many that their blood pressure is too high, but it’s better to learn about a potential problem before tragedy strikes.