@SubmarineGirl
I just went through this , pulled or stained something behind my knee
I heard and felt a pull as I was stretching my leg while sitting down in chair, and bam I got a bad leg cramp and then next day I could hardly walk on it. Took a good 3-4 walks for it to feel better,
I still have to be careful not to tear it again.
If you torn something bad enough you may need surgical intervention. I hope not, feel better and stay off of it as much as you can.
Tendon Pain Behind Knee | 6 Possible Causes (painbalance.org)
I would get a good knee brace and wear it , mine was getting injured during my tossing and turning at night believe it or not.