Why don't things in dreams traumatize you?

the other night I had this dream where I was driving a convertible car along a frozen lake when suddenly the ice broke up and the car fell in to the ice cold water, my arms went Numb so I couldn't get my seat belt off and the ice cold water (it was ice cold I can remember the sensation) started to washed over me completely, just before it did I can remember thinking "I can't get my self free there is no one is hear to save me... I'm going to die" then my head went under and I woke up, you know what I fell looking back on that dream now? pretty fine to be honest don't get me wrong it's not a pleasant memory but if something like that happened to me for real I'd be a wreck... so why aren't it? it felt real, I thought it was real as it happened, I can still remember it perfectly, why aren't you traumatize by things in dreams if you think their real