If you’re reading this any time after lunch and you’re not dead, well done. You have, in the words of Professor Russell Foster, a chronobiologist, “survived the most dangerous part of the day”. Chronobiologists study the body’s various internal clocks. In this documentary, specialists reveal, among other things, that you are three times more likely to have a heart attack between 6.00am and noon, when the blood is stickier and the vessels stiffer. These are the “danger hours”.

Why are you more likely to have a heart attack at eight o’clock in the morning or crash your car on the motorway at two o’clock in the afternoon? Can taking your medication at the right time of day really save your life? And have you ever wondered why teenagers will not get out of bed in the morning?

The answers to these questions lie in the secret world of the biological clock.