Fish doing backflips??

I have seen my pearl and zebra danios do that, too, on my plants. I think they're just getting a quick bite to eat, but perhaps someone with more expertise has a better answer. You should make sure they're not rubbing against the gravel and decorations a lot to soothe an itch (i.e., "flashing") from something like ich. Judging by what you describe, though, there is probably nothing to worry about. In my (limited) experience, this is healthy behavior.