That's a bit of a problem. We had a very high ranking position on that term #5 or so. Then we suddenly dissappeared on every single term. We're trying to get in touch with Google on this issue - just to make it clear - we did no spam / blackhat.
Google is constantly testing sites and seeing which ones perform well.
I wouldn't be worried unless its still not back in 2-3 days.
I'm not a fan of it (non-native UI) but it does the job and I got it for free through my company.