I've gotten a little hypomanic with good news too. Any stressor is a stressor, be it positive or negative.
However- I totally agree that you should enjoy the good news! Sometimes happiness is just happiness, it doesn't have to be pathologized.
I personally am in a similar situation. I'm adopting a dog, which is so exciting! But then I find myself getting anxious and perseverating about all the other dogs in the shelter that I can't take home. That and the combination of the bizarre weather change here in NYC is making me feel jittery.