There was a 1-2 year period where I pretty much refused to look at myself in the mirror. It's not a path I recommend heading down. Most directly it will detract from a healthy sense of responsibility for maintaining your physical appearance. What's more troubling, though, is that this lack of responsibility will likely start to seep into other areas of your life, so that you'll feel less responsible and less connected to the world generally. It's not a healthy pattern of behavior to fall into.
While compulsive mirror-checking is to be avoided, the opposite extreme of avoiding mirrors entirely is just as bad.
Break the habit -- force yourself to look every now and then. The more often you do it, the less frightening it will be. And if you don't like what you see, take some reasonable steps to improve your appearance (emphasis on reasonable -- don't run out and get extensive plastic surgery, as it could irreversibly make matters worse). Wear makeup, style your hair; even if you don't like the way that you look, you can at least try to make the most of it. Dissociating and letting yourself go certainly won't help matters.