What's wrong with me?

[tolbiny]

Normally a long ass psycological list would follow said question, however today i am only interested in one particular sympton.

I am tired all the effing time. From the time i wake up in the morning i am tired and constantly think about (and take) naps.
I am not terribly out of shape (5'10", 175)- not entirely unactive- i bike to class and back 4-5 times a week (12 miles round trip) and take my dog out for a walks - anywhere from probably 1/2 -1 1/2 hours a day. Otherwise i don't do [censored], cause i don't want to- i would just rather sit or sleep. Is this just me getting older (26)? My diets alright, some green crap on my plate next to a chunk of dead cow/chicked most nights.