My parents had a Chesapeake Bay Retriever, he was sort of crazy, though quite adept at detecting security threats like the mail man. But I could see how one, with proper training, might become a service dog. Pat's mission was to save the world from pine cones by destroying every one he could find. I think his record was 7 in his mouth at one time. He was also addicted to bodies of water & would swim until he collapsed.

Now that our 14-year-old Lab needs a seeing eye person I'm much more sympathetic to those who require service and/or guide dogs, whether their plight is evident or not. (ETA: I am by no means making light of people who require assistance/comfort animals by bringing up my dog's blindness...simply trying to bring some levity to a topic that often becomes contentious.)

Back OT before the inevitable close...a friend who's a former Red Coat once boarded a Great Dane whose owner had seizures, or maybe fainting spells, that the dog would detect then lean against her as an alert & also so she could balance on him. IIRC she purchased an extra seat for the space needed.