Let's say that the real you died last night in their sleep. The real you was also part of an advanced secret government cloning program. After he/she died, they removed the real you from the bed and proceeded to make a clone. This clone is YOU. Upon completion of the cloning sequence, you were placed in the bed of your predecessor. And because you were the clone of the final version, you share ALL of the same memories.
You think that you are the real you because you have all of the same memories as your predecessor, but you are actually just a clone. The cloning process having been made simpler because they studied the genome of your predecessor in great detail before he/she died.
Finally, you find out that you are really just a clone, and none of the experiences you've ever had actually happened to you. They are merely memories from the real you.
-How would you feel?