The Biomatrix.net is creepily similar in intent to Building Batman. They claim to be
a website that takes self-improvement to the next helping you to become stronger, faster, better and smarterStrange that these self-improved and smarter people forgot a word in their intro. sentence, isn't it? ("...to the next [level,] helping...").
Anyway, in the article Become Ambidextrous, the author notes that his head "feels sort of tense" and suggests that it may be a placebo or a coincidence. Strangely enough, I've had the same sensation since I started using my left-hand and thought it was a coincidence myself. I also had the same amazing improvement in the first days of practice. Personally, I thought that this would be much harder than just breaking the habit of using my right-hand but now I already feel that that is all it is - being right-handed is just a sloppy habit. Here's a notable blog about someone else who's decided to kick the "right-handed habit".