Nobody ever needs to sit to clear their head. He hit a home run on Monday. He probably was distracted by being with so much family, maybe. Also, he's the DH. He can meditate for two hours of every game. Could probably microdose if he wanted.
Thomson keeps playing Kepler and Castellanos because there's a chance either of them can run into a little offense or (more in Nick's case) get hot again. If they can't get some power from the RHBs, especially, it doesn't really matter how good the OF defense is probably. Hopefully Bohm coming back helps a little. But otherwise the team will win with pitching and the 1-3 hitters or they won't.