I've been running regularly (once or twice per week) for four months, wearing the same shoes each time. However, the last two times I've run, my left foot has gone numb about 2 miles into the run. I've been able to keep the run going for a couple more miles, but I need to cut things short around 4 or 5 miles for fear that I'm going to roll my ankle.
I'm wondering how this problem could surface now, after months of running without issue in the same shoes. I should add, the bulk of my running takes place on a treadmill, because it's cold outside (where I live).