Of course, We're happy to provide our own feedback and give you a few sources that could help. So your first question was about how depersonalization feels. Within the context of a book, it would be better explained as if a character was viewing themselves in the second person, but for a better more in depth explanation. Depersonalization is commonly explained by the feeling and experience of someone watching themselves through a third person point of view. As of switching between alters, a lot of things can trigger a switch between them, such as smells, sights, feelings, noises and tastes. Because of it's nature D.I.D has the same triggers as P.T.S.D. The switching process can vary, sometimes it can be quick and seamless, other times it can be a long and very draining process, but most of the time it's a mix of the two. Active alters are a bit more tricky to explain because it's different for everyone, usually the closer that someone is to their alters the more that they can remember and/or get insight on, but most people describe it as gaps or blank spots within their memory, usually lasting hours but there's really no telling how long a switch can last. For more information of these topics there's a wonderful YouTube channel named DissociaDID, she's very helpful and much better at explaining this than We are.
