I have massive sleep issues. My body refuses to sleep before ~3 am (I tested this for many years through various different experiments).I usually sleep around 12 hours sometimes a little more (My maximum was I think 20 hours at once). If I somehow manage to fall asleep before 3 am, e.g. by staying awake the whole night until the next day at 6 pm or something, I usually sleep around 6 hours, meaning I wake up in the middle of the night