They always have the right to ask for another opinion. They also have a unique construct in the Canadian Forces that is in various forms resident in private institutions across the country. We affectionately refer to it as the chain of command.
The chain of command has an abiding interest to make sure that the morale and welfare of their men and women is looked after, and that chain of command is a very powerful champion in advocacy for their morale and welfare. If they do feel, for argument's sake, that they're not being heard or not diagnosed well, they have a very quick, very active response mechanism to ensure that there is sober second thought provided as and when required.