Worry is the greatest drain, as the body is fighting the issues endlessly, with no end. Your body was not designed for this. It was designed for fight or flight, not endless battle. In your primitive past, when presented with challenges, you either fought off the threat or were eaten or destroyed. The matter was over quickly. Modern society presents situations that are neither over quickly nor destroy quickly. Thus the battle stage is drawn out endlessly, and the soldiers grow weary. Put the battle to an end somehow, if only by deciding not to engage. If there is nothing you can do at the moment, and you can have no effect on the outcome, then put your weapons down. Be at peace. Smell the roses.