So far, it doesn't hurt, it's just a little annoying. A couple of weeks ago, my husband and I drove to Alabama to visit members of his family. During the long drive, I knitted socks. The armrest in the car could definately be the culprit. Thanks for mentioning it.
What really bothers me is the fact that it now happens when I do other things. We are in the process of painting our house, and I had to stop, hold my arm down, and wiggle my fingers to get the blood going again. This happened frequently while doing the trim, and other brush work.
Also, I have a cat who loves to sleep in my lap while I knit. This causes me to hold my work up more and a little to the side. I'm sure this positions doesn't do much to help my situation.