Everything you feel is probably so similar to what everyone else has felt prior to the move. I like to fluctuate back and forth because it keeps me on my toes...and my emotions can just rock out!
I have a feeling that once the airplane leaves the ground you'll be feeling the high (no pun intended) from the anticipation of an entirely new lifestyle. Remember to always make the most of a new experience. If you go into this with any negativity, your experience will be just that: negative. Instead think of all the possibilities and all the positives of living in such an incredible country. Yes, it's important not to go in with rose-colored glasses, but to keep a positive outlook all the while.
I wish you NOTHING, but the best!!!