I can hopefully clear up some of these ideas thanks to my experiences.
Regarding myself, I'm not about to show my power level too much so I'll keep things a bit vague. First, as a kid I was diagnosed with a mild mental disorder. The exact definition of this disorder is debated, but I don't doubt this diagnosis. When I first found out, I doubted it, and hated the idea that I wasn't normal. Eventually, I learned what some of the quirks were, becoming more self aware in how it affected me and learned how to deal with it rather than try to ignore it. Now, you wouldn't even be able to tell I have it, and if it wasn't for the way I act in some cases, I would have even considered myself possibly "cured" of my behaviors. In recent years, I've considered the fact I may have a form of PTSD as well, although I keep telling myself I might be exaggerating and I'm not about to self diagnose myself with it. The reason comes from my time in the military, but not because of war or anything like that, although I was close to frontlines. It's actually just due to years stationed at a place that was physically and mentally exhausting, and that I occasionally still have nightmares of and in general just get highly stressed if I remember anything about that place. So take that experience how you will.
Regarding DID? Let me tell you right now, 99% of people claiming it are BS. I've met 2 such people before, and while the first one never claimed it directly to me, they did claim it to 2 of my friends, one who believed them and another who called BS. Granted, the friend who called BS is actually off his rocker himself, for one reason or another. But my experience with the second person solidified my conviction that the first person was lying. This second person I met through a friend over discord, and they were acting strange. Eventually, our mutual friend explained that this person had DID. I fully believed them at first, DMing and chatting with them that night in private, and learning a bit about them. I believed that I was talking to "3" different people throughout the hours, and that it was random, and the next day while at work I researched DID more so I could learn more about it. THIS is when I realized how full of shit they were, as I learned about how DID actually works, as a sort of coping mechanism, it's specifics, and how it's not like you see in TV and Movies, where there are multiple personalities in a sense controlling or sharing a body. After work, the more I talked to that person the more obvious it was they were full of shit and just pretending to have multiple people in their head. I talked with a couple friends about it and they told me that the person was certainly lying, and that their experience with someone who actually has it is very specific, like they might "change" every few days, but not into some other personality, just a version of them with different memories, and that they both had their own logins for things like discord and just learn to deal with the unusual way they can't remember stuff. Moral of this story is that if you ever meet someone who claims to have an alter ego that is like a kid or even entirely different person, they are bullshitting you.