I woke up with an extremely red eye. Half of the white of my eye is solid red. It is not sore and vision is fine. Should I seek medical attention?
Yes. Chances are it's probably a harmless subconjunctival hemorrhage (bruise in the eye) - maybe from rubbing your eye too much during the night or cough or sneezing. And especially without pain or blurry vision, it's even less concerning. However, you only have two eyes... If you're uncertain, get it checked out.
Red eye. Yours sounds like a sub conjunctival hemorrage. Usually from rubbing your eye, possibly while you sleep. Usually no cause for concern, the whole white of your eye will turn red then slowly clear over a couple of weeks. If you get frequent recurrances or easy bruising you should get your blood check for bleeding abnormalities.
Hemorrhage. This is almost certainly a small hemorrhage under the lining (the conjunctiva) that covers the whites of the eye (sclera). This is due to seepage from a small vein induced by rubbing, sneezing, coughing, lifting heavy weights or sometimes no known cause. It will clear in 1-2 weeks and may spread over a larger area until absorbed. Not a problem if the vision is ok and no pain.