off the original topic, i know, but as someone who struggles with sleep and will often have a strange pattern when i do during what people would regard as "normal sleeping hours", i found this fascinating! thank you! when i "fix" my messy sleep patterns and find myself tired at those more normalised hours, i'll often sleep from 9pm til about 1am, at which point i'll feel wide awake, so will get up and do something else for an hour or so, then head back to sleep til i wake up at a more appropriate morning hour, almost exactly as you said! i had no idea about this, and as someone with an interest in human history and also in sleep patterns and our brain's responses to them, i can't believe i didn't know this!