Struggling with Reality Perception

I do this thing sometimes when I'm watching videos I get used to how things work in the world of whatever I'm watching and then when I'm watching something else I forget that the rules from before don't apply anymore. I guess it's just a funny thing brains do to adapt to new situations. What's more troubling to me is when I can't tell if I'm dreaming or not. Do I need to be worried about a bear attacking me suddenly? A million spiders crawling all over me? Or am I really awake? I hate to not know, i hate even more to find out by getting attacked by wolves or losing a few fingers to a knife murderer only to wake up in the middle of the night