1. Multi-tasking is less efficient, due to the need to switch gears for each new task, and the switch back again.   2. Multi-tasking is more complicated, and thus more prone to stress and errors.   3. Multi-tasking can be crazy, and in this already chaotic world, we need to reign in the terror and find a little oasis of sanity and calm.
Take deep breaths, stretch, and take breaks now and then. Enjoy life. Go outside, and appreciate nature. Keep yourself sane.