Odd Knee Pain, Not Overuse

About a week ago I had an accident at high speed that resulted in me flying off the unicycle, essentially doing the splits with my left leg and sliding forward about 10 feet in that position. It messed up my left knee in a weird way, in that it was initially very sore after it happened, and then it was just about painless to do anything with it except bend my knee or put pressure on the bent knee (for example, kneeling on a cushion).

It has progressively gotten worse to the point that running or riding ends with a day of soreness and pain. That didn’t used to happen.

The pain is primarily in the back of the knee and to the sides. Any ideas?
Thanks for your time.

Idea: Go to a doctor.