5 days ago i was getting out of a car and it was low to ground and while swinging my legs out i felt like a charlie horse coming on but when i felt my leg it was like a big bubble and swollen. i said oh lord do i have a blood clot. i raced to the er and they gave me a shot to stop clots and then next morning gave me a ultra sound to see if i had a blood clot . Thank God i didnot have one. I now have a great big black and blue behind my knee why did this happen? did i jam or twist the vein when i got out of the car?