I'd like to argue a little bit for treating the voices in your head as real.
There is a phenomenon of "plurality" where you perceive yourself as a system of multiple people/personas with unique personalities and interests and identities. Psychologists would generally classify patients who show up this way as having dissociative identity disorder - but only if they meet the criterion of the symptoms causing distress/affecting your lives, and many plural systems seem to be just fine with it.
https://www.reddit.com/r/plural/wiki/faqs is probably a good starting point for reading about it from an inside-the-community view. (There's a plural community for essentially the same reasons that there's a transgender community.) https://smallcedarforest.org/on-transgender-and-plural-exper... is an interesting post from someone who connects plural and transgender identity. (FWIW, the one person I know IRL who is out about being plural is also trans.)
Going further back, we have stories across cultures of people who (either positively or negatively) claimed the ability to communicate internally with other personalities/identities, and occasionally those personalities would "front" (in the language of the contemporary plural community).
And then, of course, there's the case of the woman who heard voices insisting that she get a CT scan. Her psychologist, who was giving her medication to suppress the voices, decided to do the scan just to prove she was fine - and she had cancer that required operation. When she woke up after surgery, they said, "We are pleased to have helped you. Goodbye," and they never returned. https://www.researchgate.net/publication/232271307_A_difficu...
And while I was trying to find that story, I found this one, of an organization that helps people who hear voices in their heads by telling them the voices are real and helping them work through it: https://www.minnpost.com/mental-health-addiction/2014/04/mos...