Its an extremely rare disease that he almost certainly does not have, given that people who legitimately do will have distinct personalities with their own memories, and no cross-over between the two. IE, each personality has no memory of what its body did while the other personality was in control.

The far more likely explanation for your friend's issues are that he has found that pretending to have a serious mental illness draws attention to himself, and he enjoys that attention.

Anthony Padilla (you might know em’ from smosh) interviews a lot of different people and asks them about their experiences

• this is his D. I. D. video

This is a very controversial mental disorder, from what I’ve seen on discussions about it, a lot of people seem to think it’s bullshit. I’m certainly no expert myself. It’s a very peculiar disorder.

Anyways YouTube now puts little tags under videos to let you know if they are from a mental health professional, here are some videos by experts

• https://youtu.be/LR7QEkU0IfQ

• https://youtu.be/defVs3F2oVI

• https://youtu.be/XF2zeOdE5GY

And here is an about an hour long podcast of a schizophrenic interviewing a woman with DID, they go in depth about what it means to live with DID and where it comes from. (Trauma) They talk about switching/moving between the personalities/alters at 15:21.

• https://youtu.be/9NDnr3tMyB4

From what I’ve learned there are different archetypes for what the personalities manifest as, it might be a different gender/ethnicity/age etc, but there usually seems to be an innocent child personality, and a protective guardian personality, there might be a personality that doesn’t speak, and the amount of personalities someone has can vary.

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I'd ask him any questions if you know he is in therapy, it could be helpful to raise questions respectfully so he can ask his therapist for more help. If he is not in therapy, he might not be able to go to therapy or maybe something else is happening (for some reason it's become very usual to lie about having DID, or maybe it is an incorrect diagnosis or self diagnosis).

Now, DID is a very serious issue. Also very rare, since dissociation doesn't usually reach that level (we all dissociate sometimes without "fragmenting" our personality, like when we are in a car or a very long line. It is not a disorder until it becomes a problem for your daily life).

It is caused by extremely severe traumatic events, specially in childhood. It causes a person to go numb to emotions, sensations and other stuff (this is called disociation and has many manifestations) the host (the person who developed DID) is experiencing, and where alters (the "personalities") "come out" to protect the body and host from psychological damage. This is a process that takes some time to happen, not seconds, specially if the host fights to ground themselves. When someone dissociates, they can't really maintain focus on most stuff because they feel in danger, very stressed or anxious. It is also very tiring and debilitating.

Alters are created as a way to take the person away from what they are evading (not created by the person in purpose), and they can be triggered by many things, depending on the host. Alters can express themselves in many forms, and have specific purposes. They also can be "merged" with the host through a long process of therapy, or make arrangements to keep going with the most normal life they, as a "system" can.

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The friend could also have OSDD-1B, which is similar to DID but doesn't have amnesia between alters.

When you're a small child in the process of growing up, one of the things you do is integrate together all your emotional states and brain functions into a single cohesive identity for yourself. If something very bad happens to you at that age, sometimes the process of integration doesn't happen properly, and you end up with two or more emotional states that don't feel like being the same person, with different sets of memories and different sets of cognitive abilities accessible in each. That's DID. There's a few related dissociative disorders (such as OSDD-1B) which are fairly similar, but differ in what's shared and what's separate between the different emotional states.

Also, some people seem to end up in a state similar to DID from prolonged overuse of certain drugs (e.g., ketamine) or by having a childhood that wasn't quite bad enough to develop DID followed by something very bad happening to them in adulthood.