We have all done silly things when we have been rehabbing, unfortunately wheely chairs have a habit of sliding off on their own. I used one myself.
I would suggest you try to see your OS, sure he won't shout at you. Best to get things checked out sooner rather than later, just in case.
I have had a HTO, so know it's not an easy recovery, I had days where I just felt like crying, but it does get better, you need to make the phone call to your OS, he may not be as bad as all that, maybe he had had a bad day too!
In the mean time, ice your knee, and rest as much as possible.
Let us know how you get on.