I'm sure it's been mentioned, but I'll say it anyway.
Traumatic head injury can cause radical changes in personality.
Likes, dislikes, what kind of foods you like, all can be changed by significant head trauma.
Doesn't nessearilly have to be severe, or life threatening. But it can't be just a little bump on the knot either.
As others have said, the kind of splitting that causes DID happens in early childhood. But that dosen't mean a traumatic event or time of great stress can't cause the symptoms of DID to become hard to ignore, and reveal itself.
Coping with chronic pain and the stress chronic illness creates drove my Dissociation back to as bad as they were when I was a kid. I thought I had put it all behind me. And so, I wouldn't have to deal with it. I may have been wrong about that, but it doesn't matter as it's all worse than it ever was before. So , no choice. Gotta deal with it.