Unless you were pronounced "legally dead" there would probably still be a missing persons file on you. I would go to police or maybe journalists and say I have information on the disappearance of Sentinel
from back in 2012. Then tell them it's me and I've come back. Wouldn't mention E.T.s right away though... I would probably say amnesia or something.
DNA testing, especially by then, should easily prove this, plus you would be identical to all pictures/video taken of you. Any living friends/relatives still alive would remember you looking exactly the same as they last saw you and could identify you.
The E.T. trip would be up to you to mention, and who knows, maybe it would be more believable decades from now. If you did talk about it, maybe you would be taken by gubmint peoples for questioning
Btw, did you get any good pics with the alien peeps on your cell phone?