When you dream some parts of your brain are very busy. The blood pressure rises and so does the pulse. But the big muscles in the body are fast asleep. Luckily, considering how crazy some of your dreams can be. During dream sleep the frontal lobes of your brain, the ones that control order, planning, time concept, impulse inhibition and many other good mechanisms, are shut off. They sure need a rest!
On the other hand the parts of the brain that consists of feelings, memories, sight and hearing are working at its maximum level. No wonder your dreams are so wild and unreal. It is this absurd mix of uncensored impressions because the controlling front lobe area is having a break. So many strange scenes can roam freely and crazy. You miss your flight; you lose your teeth and make a fool of yourself. But you can also fly like a bird and visit beautiful places.