I can tell you first hand that you are probably correct. I work constantly, either at the fire department or EMS, both can be stressful enough. Although my fire department is a paid department, we have volunteers. I end up doing a LOT of training with them, and teaching them. I am also in charge of our Fire Explorer program, which are kids 14-18, and training them. When I have those days of hours on end teaching, I am completely worn, to complete exhaustion. Its very mentally draining, and every single aspect of our body relies on our brain and it being fully functional. If your noodles are bad, the soup is nasty.