I'm in management and this business about managers all being psychopaths etc is BS and frankly a lot of whining. The underlying problem is that very few people, including some managers, end up doing work that they find meaningful, and we're all bombarded by garbage messaging about how we're all supposed to find our passion, and treat work as an act of self-expression etc etc. That isn't possible for 90% of people even in rich countries, so for most people the most reasonable thing to do is coast along and try to enjoy life outside work. That also makes for a certain number of people who just aren't good at their jobs and are miserable, and that has to be dealt with. I've fired quite a few people, and it was always because they were ultimately making work hell for other staff by screwing up or shirking repeatedly, not because I had a personal vendetta against them. If you've ever had to go through the process of managing someone's performance, spending 30% of your time on 1% of your people, and firing them, you'd know it's the worst part of being a manager and the last thing you want to do.
As for the OP, that is a very different and tragic story, and I'm sorry your illness got in your way and somehow couldn't be managed better. I've had a few bipolar people in my life over the years, and it's one of those diseases where few people understand how awful it is. I hope things work out for you.