That's because you don't remember your dreams when you wake up. You may have very vivid dreams but when you wake up, you can't remember any of it so you suppose that you had not had a dream.
Number seven kinda explains why I usually see no faces in my dreams (No, I don´t dream about Slendermen, but I just usually see people from behind or just can´t see their faces) - I usually don´t look to other people.
I once sleep walked up and down stairs the whole night and my friends dad asked if I wanted water so I took the water and continued up and down the stairs.
Sometimes I'd wake up half asleep, and think to myself 'I need a glass of water' or 'I need the toilet' but I'm so tired that I'd fall back asleep. Then I'd have a dream where I complete the task that I needed to do like get a glass of water or go to the toilet, and then wake up again. Then there is a few moments of me being conscious that I think that the task had been completed, but then I realize it hadn't.
Non of these facts are accurate because dreams usually fucked up and straight up weird.
Well thats just me...