I have ra, suddenly have severe pain in 1 knee when resting. Pain wakes me up at night, goes down my leg. Is this RA related?

Can;t say for Sure. It would take more info-for example, is this related to activity? Are you on any joint-sparing meds? Do you have any other medical conditions like diabetes? Any history of back pain? This all need to be addressed and more. See your physician to help get this worked out.