"I feel fine, so I don't need it"

The silent ones are harder, because here the feeling isn't misleading you. It's simply not connected to anything. High blood pressure, the NHS says, does not usually cause any symptoms, and many people have it without realising. High cholesterol is the same. You felt fine before the diagnosis, you feel fine on the tablet, and you'd feel fine for years off the tablet, and none of those three feelings tells you anything about the pressure in your arteries or the state of their walls.

This is the belief with the biggest numbers behind it. A study of 4,783 patients prescribed a once-a-day blood pressure tablet, with their dosing recorded electronically, found that about half had stopped taking it within a year. On any given day the ones still taking it missed about one dose in ten. Nearly half of them had at least one run of three or more missed days in a year, which the researchers called a drug holiday. Nobody in that study could feel their blood pressure. That's the point. Nothing was telling them to take it, and nothing told them they'd stopped.

What the tablet is doing is measured in decades, not mornings. A review of 44 studies with nearly two million participants found that about 60 percent of people took their heart and blood pressure medicines well enough to count as adherent, and that those who did had lower rates of heart attack and stroke and lower death rates than those who didn't. The researchers estimated that a considerable share of cardiovascular events in Europe, around nine percent, could be put down to poor adherence alone. Chapter 13 says what those numbers can and can't tell you about one person. For now the point is simpler. Feeling fine is the normal state of someone with high blood pressure, on the tablet and off it. It's the one test that can't distinguish them.

The right instrument is a cuff, not a feeling, and the NHS says many pharmacies will put one on your arm for free if you're over forty. Chapter 16 is about using it.