Space-travelers face a topsy-turvy world where up and down is nowhere to be found. Sensors in your inner ear signal to the brain not only that you're not in Kansas anymore but the familiar tug of Earth's one-gravity is missing.
Very few astronauts have what's called the "lead head"--immune from space adaptation syndrome or space sickness. Vertigo, nausea, headaches, and in some cases vomiting can strike a new arrival to space.
Moreover, the up-and-going world of commercial space tourism will likely spotlight the need for some space sickness countermeasures to be "market ready."