For 40 odd years I got up between 5 and 7 to go to work and punch the time clock in various occupations. After 'retirement' I discovered that my natural schedule is to sleep from 'about' 1-2 AM to about 9-10 AM. Days when some event calls for me to be up at 5-6 AM require effort and forced early sleep, along with an alarm & radio.

I am convinced that TV, the internet and advancing age have altered my sleep patterns permanently.