I Fell Down Two Days Ago On My Knee, Well

I fell down two days ago on my knee, well under my knee, and there is a purple/blue bruise shaped in a circle, and the middle of it is the shape of a quarter. Not bruised at all but is super sensitive, at the same time I can barely feel anything when I touch that part of it. Should I go to the doctors? Is it severe? What might it be?