Generally speaking, if you are fully aware/awake/conscious/remember everything that occurs during your personality change. ..then you can probably rule out dissociation. Many things can make a person feel completely different at a moments notice "normal" things and/or mental/neuro/physiological issues. Regardless, if this is a new experience/ symptom for you, best to see a Dr rule out physical and neuro first. And talk to a Therapist or PDoc as well especially if these changes are disturbing to you and or causing issues in your daily life functioning or relationships. Sorry don't have more advice to offer but hope everything turns out well
In the Meantime Keep Writing!