well most likely you were stressed from the previous day and then you had nightmares. Sometimes I wake up in the middle of the night with a startled yell, sit up straight but then I close my eyes and go back to sleep. When you're having a panic attack you might feel the need to "escape" or get out of the room, like how you said you went outside, but it is important to resist this urge. When you are rushing it gives your body a "heads up" that this is a dangerous situation, when in fact you were just lying in your own bed! Then, your body will release more stress chemicals to help "fight the danger". Do talk to your doctor about your concerns. But until then, assume that the physical symptoms are only manifestations of pent up anxiety. Best of luck to you!