Reflecting on the self.

Or probably a self-reflection?  Have you ever come to question one of the (supposed) foundations that your life has? The self, the "I"?
Have you ever doubt yourself in such a way that you come to doubt the very concept of I, or self?
Well, suddenly everything comes under the shadow of doubt. I am no longer sure if I do what I do because I want to.
The movies I see, the music I hear, the books I read. I don't know any longer If I search for those things on my own, or if I am trying to build a new I based on the external, and the other persons.
And it feels odd. Pretty much like a losing of identity, being totally determined by anything but me.
But isn't the self an artificial construction anyway?
I don't know, and the feeling is quite confusing and numbing...