My dose recently went up from 300 to 400 mg, too. And yes, at first I noticed I was a little klutzier than usual (and I'm not a graceful person to start with) and had more trouble finding words. That seems to have leveled off though now that I've been on the higher dose for a few weeks. I take the Lamictal in divided doses, once in the AM and the other at bedtime, so that might help you avoid the side effects.