Key points from article :
15 million people in the UK live with a long-term chronic health condition.
Study sleep-tested 16,000 adults between the ages of 20 and 74 and tracked their health for 20 years.
People with existing conditions have double risk of fatal heart attack, stroke if they sleep less than 6 hours.
Insufficient sleep was also linked to forgetfulness, stress and low mood.
Results were published in the Journal of the American Heart Association.
Research is done by the Pennsylvania State College of Medicine.
