Truly be skeptical of what's around you - pay close attention to where you are and how you ended up there. See how objects feel - is the texture of certain things "off"? Look around to see if things are distorted. Is the lighting dim, even though it shouldn't be? If you're in a house, look outside to see if you can catch the details of buildings and plants, because sometimes if you look out a window in a dream, it can dark and hazy.

People don't question reality because it feels incredibly real, but dreams also feel extremely real, therefore we don't question them either. So what's the real difference? How can you tell if you're awake or asleep without first questioning things and doing a reality check to see?