Up until (very) recently, I was also typed as INFJ. Everything you just said about being lost in thought etc doesn't mean toffee - any type can get lost in thought, and all types do. The vast majority of my own thoughts revolve around matters pertaining to the metaphysical; I care about the bigger picture first and foremost, yet I am an ENFJ. Trivial matters do not concern me, living in the present moment is nigh on impossible (no, really) and I seek to understand the nature of reality far more than I seek the company of others... yet in spite of all of this, I lead with Fe.
Strange, right? Perhaps not when you consider that I grew up with Ti-doms, but that's besides the point. The point is that you're asking a question about social chameleon-ism (new word? New word!) which is a product of Fe first and foremost. Socially, Fe can be mirror-like. If you experience this fluidity of character so much that you essentially 'lose' who you are, you should absolutely consider that you lead with Fe, not Ni. Funfact: I'm 26 years old and I've spent most of my teen years / adult life so far trying to work out who I am and what I'm about. When a Fe-dom looks within, things can become extremely confusing.
Oh, and for the record I would NEVER assume that I was an extravert. I took a lot of talking down in the end; eventually I saw sense and realised that I lead with Fe. Now, you may indeed be an INFJ (let's face it - INFJs still have a massive blast of Fe courtesy of their auxiliary) but I wouldn't be so quick to disregard ENFJ. Take a look a the following to see if you can identify:
.... annnnnd now I'm going to get a coffee, seeing as I wrote that straight out of bed