I am 24 yr old female and yesterday my knees gave way on me. Then today (19/7/2011) my knees feel like they have a build up of pressure behind my kneecaps - best described as air bubbles. I can't walk properly or bend the joints to be able to walk. If I stand or sit for too long I can feel the pressure building up and then to move or stand up (from kneeling or something) results in alkot of pain just in the knees. There is no visible swelling or bruising and to touch doesnt hurt. This is causing a great deal of pain and discomfort and last night affected my sleep. What could this be?