I'm 45 & wake up yelling due to a sudden stabbing pain in right knee.

Odd if ONLY. at that point in the day. We get into some odd positions in sleep that put different stresses on different parts. It is LIKELY that loss of cartilage on an edge of the knee causes bone on bone grinding. BUT you'd have some sypmtoos some other time. Or it is muscles and not the joint.
Knee pain. needs to be evaluated by your doctor. He/she will determine what is going on and help. Peace and good health.
Injury or infection? Did you twist your knee during your sleep? Are you running a fever? It is difficult to comment on whats causing your knee pain. The best suggestion would be for you to get a proper examination by a doctor who can then determine the cause of the pain and treat accordingly. If you are experiencing fevers and knee swelling, this could be an infection in the joint and needs to be seen urgently.