Antilogies and the subtle truth

It's weird, but each time I'm experiencing something that really makes me happy, I inevitably start getting sad as soon as I realize that I acutally am happy right then. It's like a movie that starts plotting itself in my head, taking me to a time far beyond the current moment in which I'll be looking back onto that scene as a memory, all the people in it, except for me, long gone and the happiness from then only a shadow left in my mind. I feel the sadness of this far off moment right then, when I still have everything I'm already mourning to have lost... it's so ridiculous and yet I can't help it...