i sympathize a lot with all of the symptoms. in my experience, as someone who used to work pretty hard, once you're past the cusp of 'it's all pointless' it makes it really really hard to bother.

Like you're not getting anything out of it. You don't care if the work is done or not. Nobody else seems to care. And even thinking about it makes you feel ill and horrible. Difficult situation to grind hard work out of

Disclaimer: I'm not a doctor but I've had diagnosed work-related depression ('burnout') and got treated for it. This is based solely on my personal experience:

You don't need to work hard to be burnt out, you may just be continuously confronted with tasks or conditions that are too much for you to deal with. A high stress environment. Burnout is just another word for depression, caused by a specific set of circumstances that are usually work/career-related.

Your son may have clinical depression, you can't willpower yourself out of one of those.