Desire of seeing that particular face again and again. It might get so intense to recognize her even in other faces. What follows can only be understood by who knows the feeling, so it's not much use to tell about it, especially in my poor words. Much better words have been used, like those in the song 'The Train' by Nick Cave (link: https://www.youtube.com/watch?v=4PcAO1YBYt4&index=8&list=PL7754BF6C8EF9197A) or 'Lime Tree harbor' (also by Nick Cave) link: https://www.youtube.com/watch?v=u6FVYLnxqbo

I don't remember. It happend long long time ago ...or it has actually never happend to me yet?

You feel that your real existence, feel you are living ; also by the way you are getting vanished.. dying..

You feel a dream like state in which the world around you seems to be not reality at all.

"A guy with a pin to burst your bubble?" :) (Heh... close enough...) https://www.youtube.com/watch?v=FzQBOBoPg04