Why do I sleep do much?

I don’t understand how I sleep so much. I mean I’m always the first one to fall asleep, anywhere anytime. I could fall asleep at a party like I could fall asleep at work. Worst is when I drive sometimes I tried to control myself to not sleep but minutes later I found myself falling asleep :S . I know people get tired but I and everyone around think it might be more. I tried coming up with explanation as to why I was falling asleep and here’s the only one i could think of; when I was really depressed last winter I would make/force myself to sleep. I could sleep all day (waking up here and there) but I would always force myself to sleep again. Do you think this is the reason why ? Even now when I’m bored or something my eyes tend to automatically close o_O