Because I'm insomniac, like Ganta Nakami on "Insomniacs After School (Anime/Manga)"

Sometimes I can sleep early (like 6-7 pm, after dinner, until morning the next day). But there's a day where I sleep just after the sun rises (and woke up in the afternoon), no matter how hard I tried to sleep early

For me, as long as I can sleep for 6-8 hours (early or not), that's enough