I know that feeling and, for me, it has a lot to do with an uneasiness about suddenly reappearing on the road after being absent so many months. When you're commuting every day in a medium-sized suburban town such as mine, you get to know many of the drivers along your route and they get used to seeing you there. The night before my first commute, I often toss and turn in bed wondering if that person who has been cutting his turns really close to the curb all winter is going to see me coming around the corner, or if the teenage girl who had just started driving when I last commuted has now gotten cocky enough to be taking selfies when she's approaching a STOP sign. And as an "older" commuter (55), I'll admit that I am always concerned that this might be the year I just can't recover from a winter of sitting on my ass in front of a computer all day every day.
I think the little bit of edginess you feel might actually contribute to your safety during those first few days you're getting reacquainted with the road and the road is getting reacquainted with you. Don't sweat it.