iPhone 4 accidentally restored to old phone -HELP!

the other night i connected my iphone to my mac to upload pictures, as I always do with no problem. however i accidentally pressed something that made my entire phone revert to my OLD iPhone. I still have iphone 4 capabilities (video, facetime, etc.) but all of my contacts, photos, email account set-ups, keychain items are now from my previous iphone. ??? I'm not sure what i've done, but it seems i've lost all the photos/video that i even tried to upload in the first place. Is all of that gone forever?! All of my voice notes, notepad notes, text messages - EVERYTHING- is back to 7 months ago when i had completely different hardware. ??
ANY help or advice on how to UNDO what I've done and get my old data back would be GREATLY appreciated. This is confusing for me to explain so if you have any questions please just let me know.

THANKS!!