I didn't know how tense not cycling made me until I started cycling. I mean, really, traffic is nothing for me. I get to work and to home faster if I drive, and I don't have the extra hassle of changing clothes in a public restroom.
But if I'm not bike commuting I'm just about not exercising at all, because I don't know where else I'd fit it in, and after a few days I start to get really stir crazy, depressed, irritable. I wasn't like this when driving was the only gig.