Chances are that the OP would have been fine, albeit passed too closely, if he'd just held his line. I get a lot of drivers who don't move over for whatever reason. They pass closer than I would like but not one of them have hit me or blown me off the road in about 15 years of road riding. I don't like it when they do it but as long as I can ride a straight line and keep my cool when I'm getting passed close it's not that bad. Some people teach that you should "take the lane" but I have a hard time brining myself to do that. On rural roads I do ride a litle farther out than I need to so when a car's passing me I can move over 6 inches or so, giving me a little more room than the driver was leaving for me.

But like Spiduhman above relates, some small pecentage of drivers are out to hit riders. I've once had a truck come up behind, floor it and try to nail me. That time I jumped the bike off the edge of the road into the gravel. I'm not sure how I knew he was going for me, maybe the change in engine speed.

I'm going to disagree with Pcad on this:
Having more information on what's going on behind you can help you make the split-second evaluation: homicidal maniac or typical idiot? If that means a mirror, get one. I don't use one but I have good hearing and I'm still limber enough that I can turn my head and look back out of the corner of my eye.