Major knee stiffness?!

Major knee stiffness?

I was just wondering if anyone know what may be causing my knee stiffness? Im not a very active person..i was walking a little with my mom, but with the horrible heat we havent gone in a few days. My left knee is very stiff, I can barely bend it, and I feel like something is behind my knee but I cant feel anything. So I dont know. Anyone experience this?

4 weeks ago
for the record, I wasnt asking WHAT IT WAS, I was just curious to see if anyone else had experienced it. Thanks for the answers.

Don't worry. If that's your only symptom, it's just a knee strain. You're just not used to doing. Barely bending it is a symptom of tendinitis. Probably damaged a tendon.