Questions for my readers

How is it when you are younger you have nightmeres and you wake up but when you are older you can have horid dreams and not wake up at all and then they cling to the rest of the day and you don't want to put your head back on the pillow in fear you will have thoes nasty images haunt your dreams? Why is this fear so crippling? What am I missing? The more I try to shove it away the more they become vivid....why is that?