"Switching" in terms of DID is generally a switch of consciousness, so you typically get some amnesia and lost time. It's not something you feel happening. In some rare cases, or with lots of communication and therapy, you might start being co-conscious with whoever is out, but it's experienced like a form of depersonalization.

Keep in mind DID is the extreme end of the dissociative spectrum. One of the diagnostic criteria/symptoms for BPD is dissociation, and you describe a lot of that in your earlier posts. What you think are switches might be stages of going from grounded to extremely dissociative or extreme emotional changes which can occur with BPD.