The cure for too long (really, almost any length of time) at a desk is to get up, walk away and get a lap of at least a few blocks in, stopping to smile, say hello and gossip with a random stranger, be most about a business while patronizing it for a necessary item, exercising both minor moderation and magnanimity with a midday meal, and then bobbing sedately along when a car with an extraordinarily loud sound system playing something inane but not shockingly rude or off color.