Somewhere in the middle of the night, my left foot snapped up and my calf suddenly caused me absolute searing pain. This is nothing new, it's happened before, but not to this magnitude or length. It must have been about 3 mins before the pain even started to subside. I reached down to give it a bit of a massage to see if that would help it, and I felt a golf ball sized knot in my calf muscle. This freaked me out a bit. As per normal after it happens, I can't walk pain-free all the time, just depends on how I walk, and if my calf gets stretched at all. Any idea what could be causing these?