Hi RapidFlyer,
I can't answer this question with certainty, because we are all different. But it does sound like you are indeed losing interest in many things, which is often a telltale sign of depression. Maybe keeping track of how you are feeling for the next few days would be helpful - this way you can see whether it gets better, stays the same, or gets worse.
If this concerns you though, I'd recommend seeing a psychiatrist. If you're not on meds already, they may be a good idea. Bipolar Disorder is hard to control without medication. If you are already on meds, it may be just a matter of increasing a dosage, or adding another med to the cocktail. You'll never know though, if you don't try!
Also, if you are currently seeing a therapist, making an appointment with them might be a good idea too.
And of course, please post whenever you need someone to listen. That's what the site is for, after all!