It's possible you were improperly diagnosed. It does happen as psychiatric diagnoses can only be based on reported symptoms rather than actual tests.
However, as the above poster said, it is possible for it to lie dormant. Mine was fairly dormant for 5 or so years (off meds, bipolar type I), but I've had it come back with a vengeance the past several months. It can and does happen.
Be sure that even though you feel fine now, you do everything you were doing before to help regulate things: avoid caffeine, keep your sleep schedule consistent and get enough sleep, track your moods/symptoms, etc.
Get help at the slightest sign of a symptom--not necessarily meds but at least therapy. I really wish I had at the beginning of this whole cycle as I might not be where I am now if I had, but I'd abandoned symptom tracking and became somewhat careless, allowed myself to get into an extremely stressful life situation (full time job, part time job, and full time school) and there she went.
also depending on the type of bipolar symptoms can lie somewhat dormant. you may have mild issues in between. just stay aware of your moods...hopefully you'll be fine un-medicated :)
Misdiagnoses are not uncommon.
None of us to my knowledge are psychiatrists but it can be dangerous to self-diagnose. Only a competent psychiatrist can provide you with well-informed opinions having taken into consideration all the necessary aspects in your history.
I hope you find relief fast.