Jen's got it right. The youngish bachelor-you has to die symbolically if you're going to become the new man you'll be when you're married. Anybody who doesn't feel some fear, even paralysis, at the prospect of the sacred commitment of marriage (even if you don't believe in God or religion, love has that much power), is not going into the changes with his eyes wide open. Talk to some of the older men you know who have been married for some time. Some of those your age might be dismissive about it, but the more sensitive ones have probably felt something like what you're feeling.
Jen's also right to suggest that you think about your bride-to-be. If you have known her for less than a year, you might be marrying too quickly. For it usually takes at least 6 months of steady exposure to start having some of the personal frictions and different goals and values that can become standing conflicts for the entire life of your marriage. That's not a bad thing, because it's inevitable. But if you're not aware of anything, or you just see a glimmer on the horizon (like she's Catholic and you're uninterested in religion), then you might be a little to blind to what's coming in your future together, so your paralytic fear could be a signal that you either need more time, or need premarital counseling, esp focused on your inevitable differences and how you'll learn to manage them.
It's also not crazy for a young man to be frightened of the prospect of becoming responsible for the life of both his wife and a child or two. If your experience with your own parents makes you feel like you're not sure you'll want to be a father ('cuz yours was not a good role model), or that you will avoid every argument like an STD, because your parents' arguments were SO endless and so destructive for everyone around--then you're going to need some training in fatherhood and/or marital disagreements, and that might mean you'll need individual or couple counseling some time in the not-too-distant future. But marriage is the best emotional finishing school we have, so it's not something to avoid like an STD.
Marriage is called a sacrament, because if you recognize it as an experience that's larger and more unpredictable than anything you've done before, you'll realize that you should be overawed by it, but it's as rich and interesting as birth and death, so it's worth the risk.