My knee popped out...?

its happened before but didnt hurt this long it happened about 9 hours ago. I can hardly walk and it feels weak and hurt and im so scared im gonna wobble and its gonna pop out again. it hurts on the inside-side of my leg. any ideas of what happend. do i neee to get it checked out? crutches? i have to march in a band for a parade tommarow...i dont think thats gonna happen. HELP!