For quite a while now I have been experiencing a large amount of eye tiredness that starts just an hour after I get up, and goes through the entire day. In addition, the muscles above my eyes, around the forehead, hurt as if I had been awake for days. The combination just make me feel exhausted (to the point where my eyes will close without me having a say in the matter), though I have plenty of physical energy, and mentally I am fine, though the aching in the muscles gets me off track.
As far as physical activity, I bike around 30 miles a week right now. I am a computer science major, so I spend 3-6 hours a day in front of a computer. I do not wear glasses of any kind, eyes are very close to 20-20 (I think my left eye is just barley off).
I would closely relate what I am experiencing to the same feeling you get after looking at a screen in a dark room for 8+ hours.