I had this happen to one knee then a couple months later it happened to the other knee. It will happen everytime I crouch drown and pivet ever so slightly. I dont take for granted things like airing up my tires, working around the house, playing with the kids on the floor... It can all lead to more knee damage. When the pain originally happened I went into the ER on the 2nd occurance as it was more painful than the first. They had not idea what it could be after checking x-rays. Im guessing I need an MRI and surgery, but Im not in a hurry to do that. I am still researching this now to find out exactly what happened to my kinees and what it will take to fix.
You might have stretched or pulled something or it could be the beginning of some type of arthritis. Have it checked out with your doctor.