I just slept from 7 am - 1 am, coming to a total if 18 hours.
This come about from staying up all night and all of the next day and play video games until 7 in the morning. So I went to bed at 7 am, was pissed off when I saw someone was calling me at 9 (which I assumed to be am), and realized after silencing the call that it was 9pm. However, I was still tired, and went back to bed, and didn't wake up until 1. 18 hours. I am the king of long, non-drug-induced sleeping. Thank you.