Coming off effexor (older version of pristiq) was the only time my actual mood shifted from actually manic to depressed muliple times a day. It was a rollarcoaster but due to coming off meds. It lasted around 4-6 monthsas i was taken off so quickly from such a high dose. My pdocs nearly changed my diagnosis as bipolar very very very rarely presents itself in that form. But once my brain settled so did the mood swings and my diagnosis stuck.

Generally true bipolar swings can take a few days (there are warning signs etc) and the swing has to last more than 2 weeks to be diagnosed as an episode.

I'd say your experience is cos of all the stuff going on in your brain at the moment (med withdrawl, ect etc) and it will pass. Goodluck.