Describe space sickness?

My theory is that the brain is trying to integrate many sensory conflicts -- what the eyes and the rest of the body are given -- and it all doesn't add up. For decades, they have taken the systems approach, such as studying the vestibular system, claiming you can not study the brain. I disagree. We have been studying the brain for centuries. You can ask people, "Is the floor always your down?", "Where is the Earth?" Some people have a sense of where Earth is and some do not. You look at their symptomology. You ask 100 questions: What do they sense, what's important to them, their reference points, their orientation. Then you begin to get a feel for the phenomenology.