If you read Mathew Walker's book, Why We Sleep, you will start believing that virtually every disease in the body owes its origin to lack of sleep or sleep related disorders. This is the bane of popular books written for mass market consumption that go overboard to stress a particular point.
Having said that, sleep is an integral part of our daily lives and both, lack of sleep and over-sleeping have deleterious effects on our body. How we sleep, where we sleep, when we sleep, with whom we sleep, are all important issues that affect our health in the short term and our healthspan and lifespan in the long term.
Over the next few months and years, I will keep revisiting this topic. For the time being, let us address some basic questions and answers. A lot of the information is taken from a review article by Dr. Michael Grandner .