And it's not because Freddy Krueger is invading the subconscious. Doctors have long known that early morning is a prime time for heart attacks. Quite why this is so has always been a puzzle.
Dreams occur when individuals display rapid eye movement or REM, mostly in the early hours.
According to a report in Nature Medicine, Dr. Peretz Lavie, head of the Sleep Laboratory at Technion-Israel Institute of Technology in Caesarea, Israel, found that the blood vessels become constricted during REM sleep, reducing circulation in the extremities such as fingers and toes. In monitoring the sleep of 26 subjects, the physician found that blood flow was significantly lower during REM sleep. Lavie's discovery was an unexpected result of a study designed to look at sleep apnea, a disorder in which a person frequently and briefly stops breathing during sleep. The physician believes constriction could make the heart work harder to pump blood through the vessels, triggering an attack among high-risk individuals. Now we know why they say the darkest hour is just before dawn.