I walk fast, too, and I often run into things (door jambs and tables, mostly). I have to force myself to slow down when I'm with other people who don't walk as quickly as I do...slow walkers kind of annoy me. I like what someone else said about people don't seem to realize they'd get to their destination faster if they didn't walk so slowly. Exactly.
I don't know if this is related--in my dreams, I often run instead of walk. I'm always alone in my dreams when I run so no one's having to keep up with me. I like it! And in real (not dream) life when I'm anxious, I often want to run. Sometimes I go for a run if I'm especially anxious. So perhaps, for me, walking fast is related to being anxious on some level, even though I don't think it's a conscious thing and I'm usually not feeling anxious at the time.