I recall simply being unable to wake up for first period at 8am most days, in late high school. Waking was painful and nothing felt better than sleep. However at night, despite efforts at good sleep hygiene and consultation from a counselor, i couldn’t get to sleep before 11 or later. My grades and mood suffered greatly, as did the relationship with my poor mother. She battled with me day after day, first thing in the morning, to go to school. The first few years of college I did not schedule any classes before 10am and had effectively perfect attendance. Mood problems faded as soon as high school ended.

Even today, in my 30s, a day or two with poor sleep will make a noticeable mood dip regardless of circumstances.

But as an older adult, I naturally wake up at 6:00 every morning. It was the same for much of my childhood except a few years of high school. So perhaps this was a developmental thing.