The www and non-www versions of the same website are considered different websites by google (yes, google is retarded, we all know this by now), so if you were ranking for both versions of the website then this explains why your indexed pages, backlinks, and keywords are growing (you've basically added the goodies of both versions of the site, together).
But the reasons for which your traffic decreased could be many, but 2 reasons that I can think of are:
- it takes time for google to figure out what the hell just happened (so you should wait 1-2 months for things to get back to normal... well, to the new normal anyway since you've merged "2 sites" together in what google is concerned)
- some / many of the pages have the same content and target the same keywords and by putting all of these pages under the same website (again, in what google is concerned you've had 2 different websites but now you only have 1 lol), so they're cannibalizing on each other and this confuses google which, in return, de-ranks all of the conflicting pages.
That's why I think that you need to wait for the dust to settle and then things will either get back to normal or, if they don't, you need to start 301 redirecting the hell out of the poorly ranked pages to their better ranked copies... actually, redirect the non-used versions of the pages to the version that you'll be using from now on (which is the non-www version, so 301 all www versions of the duplicate pages to the non-www version of the pages)
Or (and I think that this is actually better), add a canonical tag to the non-www pages, but do this after the dust settles, like I said, because before this happens you won't know which pages will rank and which ones won't