Ligament, Tendon or Muscle behind my knee pulled? What should I do?

Yesterday I was boxing and I suddenly felt like somone gave me a dead leg in the back, I fell down to the floor staight away and could'nt get up by myself, was really painful! Its not the muscles close to my thigh, its to my right, like the edge of the leg behind the knee.. I can only seem to get my leg so far back and forward, limited limitation of movement before it hurts. Sudden pains when I move it in a certain way in discomfort.. I have a banadge on it, some deep heat.. Just want more information about what it is and what actions I should take, thank you,