As teenagers, it isn't uncommon to fall in love with a movie character and thinking about the actor non-stop. What makes Avatar so special is that it leaves everyone feeling in love. 

Not with the actor or actresses, but much more so with the beautiful world it portrays: Pandora!

It isn't uncommon for people to watch the movie and come away with a thing the Germans call "heimweh". The exact translation is "homesick" but it just doesn't carry the same weight as the German version has in german.

Here's how the Urban Dictionary describes the Pandora Effect: 

A condition causing one to feel a strange mix of emotions (which may include awe, disappointment, giddiness, emptiness, warmth, and most of all depression) after watching James Cameron's Avatar movie. For many it has changed the way they see the world and life in general.
There are several treatments for someone who has the Pandora Effect; go see the movie again and again, watch youtube videos about Neytiri (or anything Avatar-related), and going to Avatar-Forums.com to find further help.
*walking out of Avatar*
<Guy A>: Mannn, I wanna be a Na'vi... with Neytiri...
<Guy B>: I'm sure there's someone like her.
<Guy A>: But I want HER in her blueness.
<Guy B>: Dude chill, its just a movie... Me toO! *sniff*
<Guy A>: *sniff* I know... looks like we have the Pandora Effect...
*goes back for another showing*