People with Borderline DO dissociate. As well as have borderline psychosis symptoms. As can anyone, especially with any kind of trauma or stressful history.

I dissociate all across the different types of dissociation. But I do it far less than I used to because of all my ongoing work in therapy.
How does it feel? Now there's a question! Depending on the situation, I can feel blank or elated or frightened, and if a dissociative flashback is involved, threatened, aggressive and physically smaller.