Well summed up Gladders, I agree pretty much word for word.
I have witnessed first hand what mental health issues can do to people and it can absolutely be as debilitating as a physical injury.
Sadly the pisstakers give the majority a bad name.
I think ‘mentally challenged’ (probably not considered a PC term now but I know what you mean) would fall under disability as it would be classed as permanent. Mental health issues often fluctuate day to day or even hour to hour.