Hi!
Please please please take this with a grain of salt. I don’t have dissociative identity disorder, but I do research for the sake of writing respectful and honest narratives relating to the disorder. Sometimes I go into DID spaces online to see the terms in use, so that if I write a character who uses the terminology accurately I can know what to write.
In online spaces, when someone asks ‘source’, it’s likely they’re asking about the source of the original work a fictive alter is based off of. Not the trauma that caused their split or anything like that, but the origins of the fictive.
Let’s say for example that someone with DID felt they needed the traits of a character like Sonic the Hedgehog when they were a child. They saw his headstrong and confident demeanor and thought they would live a better life with those traits, so an alter named Sonic and having those personality traits split off. Later on in adulthood they know they have DID and all that, and are asked, “Source?” when in relation to their fictive. Even if their fictive’s name might have changed, they may still answer “Sonic the Hedgehog” because that’s the origin point for that fictive alter.
While I understand diagnosis can be difficult and really stressful, I highly recommend seeking out professional assistance if you do believe yourself to have dissociative identity disorder or OSDD. However, I understand that not everyone has money, and the person who knows you best is yourself. There’s no harm in potentially being inaccurate in your self-diagnosis, so long as you eventually find your way to the correct answer.
I hope this helped, and have a good day!