I was thinking about this during the day. And I think that there is quite some reasoning behind it because of the caffeine itself. Caffeine is known to make you stay awake and become more aware of things. It's pretty hard to go to sleep with a lot of caffeine, but if you somehow manage to, the caffeine will probably keep you very aware of all ur surroundings, and if you're sharp you might realize taht something is wrong and that you're dreaming. Even though, I read that when you are dreaming, anything at all seems normal. However, this one time i had this lucid dream which was weird. I realized I was dreaming because i opened my wallet. And earlier that day, I went to the supermarket, and I remembered how much change i got back exactly. And I think when i opened my wallet, I either had way too much or way too little money, and thats when i realized I was dreaming.