I have a very swollen knee. This happened 18 months ago on the other knee, but I felt at that time it was due to an over-stress situation (hard bike ride after a 5-year "break" in riding). It went away after 24 hours. This time the only "stress" was due to a fall, but that was 2 weeks ago, and it has felt fine over the past 10 days. It came on suddenly yesterday, swelled up, sore and couldn't bend knee. It seems to be getting better, almost 24 hours later.