I think its just because they are unintegrated. Like in a non-dissociative person they may still experience all of those feelings (because I think its pretty normal to have many different feelings about upsetting things) but be able to "own" and accept all of them. Like they can say "I feel this and this and this as well!" Whereas with traumatic dissociation particular emotions might be attached to traumas from the past, so it isn't "safe" to feel them or own them because it brings up stuff that is disowned and repressed. So they are "disowned" as "not real".
I do this all the time! So much of my stuff is "not real". It makes it really hard to know what is valid and what is not but I am learning to see that all of it is valid and real. (Slowly!)