I don't exactly remember the first time I ever slept "funny" and woke up with a kink in my neck. I do remember the time when, in a n effort to save a few bucks, I tried to do some plumbing in my home. After lying on my back under the kitchen sink for an hour or so, I could barely turn my head or raise my arm the next day because they were so stiff!
This did not happen when I was a boy. Getting old sucks and there are constant reminders of it on nearly a weekly basis now that I'm 45.