Is it normal to need a lot of alone time?

So as I’ve posted about previously, I have a street canvassing job. We go to sites around the city in which I live, and work for a few hours and then we all go to lunch. I always think up some excuse to have at least 15 minutes to myself during that time, during which I listen to my iPod, play a game on my phone, have a cigarette, and just tune out. If I don’t get that time I feel really keyed up and on edge for the rest of the day.

Is it normal to want to do this? I’ve never met anyone else who needs to take breaks from people. It’s not that I don’t like my co-workers, I just can’t be without my alone time. Thoughts?