The joy of losing yourself

I am happiest when I cease to identify with myself. When I am actively engaged in a project (or entertainment) and find myself grinning and humming with no thought of "I," it is when I recharge and discover the world as positive.
The paradox is to consider who you are making happy: if the "I" goes missing when you experience joy, what is doing the enjoying? Perhaps the "me" beneath the ego.