Nikki - While your symptoms certainly fit with hyperventilation syndrome, (and yes, it can happen even when you think you're relaxed) if that is the cause, episodes should resolve quickly with proper paper-bag breathing. (Tips - keep the bag tight around nose and chin, and breath SLOWLY and SHALLOWLY into the bag). Symptoms should resolve within 5 minutes.
That being said - given your unusual past medical history, just wanted to give you these references for information on hypokalemic periodic paralyses. These can be genetic, or due to hyperthyroidism (which can be autoimmune, hence the potential link to your previous health issues). Your symptoms as you describe them aren't quite a perfect fit, but the fact that they gave you potassium makes me think it's a possibility. The references include a list of possible triggers, like alcohol, stress, high-carbohydrate meals, etc. - perhaps you will notice a trend if you think back over these recent episodes. Anyway, I would print those references out and discuss them with your doc. It's a rare diagnosis, which makes it unlikely but also makes it likely to be missed if that's what you have.
