@ejstocker
Did you hyperextend, twist or injure your knee recently? Could you have injured soft tissues in your knee? Your symptoms seemed to come on suddenly. You may have irritated a nerve/blood vessel and surrounding tissues.

I once was dancing and felt a crunch in my knee and ended up with significant swelling, couldn’t bend my knee, pain, etc. and ended up having inflamed plica tissue. I couldn’t walk on my leg for a while.