From a New York Times story by Alisha Haridasani Gupta headlined “Why Does My Sleep Become Worse as I Age?”:

Q: As I’ve gotten older, I’ve found it harder and harder to fall and stay asleep. Why is that?

Dr. Abhinav Singh, medical director of the Indiana Sleep Center and a sleep professor at Marian University College of Osteopathic Medicine, likes to answer this question with an analogy. Think of your ability to sleep as though it were a car, he said. As it ages and clocks more miles, it begins to fall apart; it needs more repairs, and its ride becomes less smooth.