Dreams

So after tossing and turning last night I finally fell asleep this morning. I had weird dreams all night but a good one this morning.
What I am getting at is this:
Why is it when we have bad dreams and we fall back asleep they pick up right where they left off. Yet when we have good dreams but wake up. Then when we go back to sleep it will never pick up where it left off.
I remember a few weeks ago, I think, I had a dream about having a dream. That was weird. In my dream I was actually telling myself to wake up. I have had that a few times. The dream is bad and in the midst of it I hear myself saying, "wake up, wake up." So weird.
Just some rambling here. I am trying to wake up....