Why must i sleep this long?!

Okay, so, one day over break i decided to go to bed after about 18-20 hours of being awake, and see how long I could sleep for at maximum (i need a life lol). Turns out I can go about 16+ hours sleeping (with waking up every now and then but being well enough tired that i can go back to sleep) and it is very hard to wake up for school and other activities if I havent had about 10 hours of rest. I've been like this since I was about 8, anyone know? I heard this is caused by adolescence but that isnt til the teen years I believe. Thanks in advance.