Good post.
You're right, the now is a culmination of the past, present and future. It's all there is.
We are what we think, negative thoughts bring about negative feelings. If I dwelt on the past I would be absolutely bonkers, I've screwed myself up for days doing that. That's why sometimes when I don't feel the best or have negativity creeping in, I'll fake feeling better, fake smile, fake happy thoughts, whatever it takes, then before I know it I feel better.