I don't know that I would call what the OP describes as "an episode" unless the rapid switching continues for days. Sounds more like mood lability, if isolated, unless particularly severe. Many people with bipolar disorder experience mood lability. Many drunk people behave as described. Unless key borderline personality disorder symptoms are usual for a person with such mood lability, that could be ruled out easily enough by many doctors. For example: Abandonment issues common at times? Pattern of unstable relationships? Rapid changes in self image/identity? Often feelings of emptiness in life?

The above are some extremely primary BPD symptoms, not in a bipolar disorder symptom list. Other symptoms not mentioned are a bit more similar to bipolar disorder. If a person says "absolutely not" to most or all of the questions above, maybe borderline personality disorder is not so likely. Any concerns should be discussed with a doctor and/or therapist.