As stated above, I'm a night owl myself and tend to have a pretty off kilter sleeping schedule. A bunch of things have contributed to that - I've got ADD and have been on stimulants for most of my life, I worked as a game dev for a few years which involved months of overtime where we'd often work 12hrs three times a week that played absolute hell with my sleeping schedule and still plagues me to this day - lastly, I'm light sensitive, I can't comfortably see and operate in full daylight.

I can't say for certain where my night-owlish self comes from, but it predates taking stimulants and working at a game dev company - so maybe it's a side effect of light sensitivity or maybe it's a neurological thing... or maybe it's just a natural clock thing.