You probably haven't had enough physical exertion in your day to drain off your energy, and your brain interprets mental focus as a sign that there's something

You probably haven't had enough physical exertion in your day to drain off your energy, and your brain interprets mental focus as a sign that there's something to be anxious about. Sure recipe for tons of nervous energy. The suggestion to exercise to physical exhaustion is a good one. I usually don't have to go that far, though. Even walking a couple miles usually takes the edge off and gives the brain a chance to wander into other paths. Doing something else that's almost entirely physically oriented can also help - a craft project, cooking, etc.