I'd call that quite a feat.
Dunno, if you're younger and you're moderately fit and train for a few weeks, you should be able to do the same, it's just a lot of effort. That said, my school was fitter than most people as side of mountain, so average fitness of our class was a bit above normal, plus Germans are very much into having "proper" PE (as in super competitive swimming, athletics, gymnastics, etc. and I am not really great at any of that, so was average at best, while in other schools I would probs be above average, just based on me playing e.g. soccer with others at uni and seeing how unfit/unable to run for longer a lot of people are).
Sad to to say that my first boss claims to have been expecting me to jump out of a window or whip out a knife at any moment.
The issue is that most people that have mental illnesses are not really integrated into society, as in you won't often meet people that are mentally ill as they'll be e.g. kept at home.
My 1st grade teacher's son was diagnosed with schizophrenia, started off beginning of second year, he was a really good student, heading to uni, I met him in 1st grade and played chess with him. By the end of the second year he basically couldn't leave the house anymore as he got super scared randomly, one time it was just shadow cast by a building across the field. I was pretty young, so didn't understand why he was freaking out.
I did meet him a couple of times since then, always years apart, and he always recognizes me and I not him, he's basically stuck in limbo is the best way of putting it. For someone like him, he would be the case where he would jump out the window, take a knife etc. if something freaked him out, all differing degrees.
Then take someone like my grandparents, Alzheimers and dementia, was just a case of my gran at random points talking intelligibly, then other cases like two class members in school that were bipolar where one ended up cutting herself randomly, the other just did crazy things like cheating on boyfriend, crashing a car, etc. until they got her meds right, with the biggest issue being that between 15-19 the dosages needed to be adjusted but you don't know until it works.
Just a huge range in regards to mental illness and no two people are alike, and South Africa is worse than a lot of other countries, still has those prison like mental asylums and stuff, it's not nice.