The moon was seen over Paris, Dec, 15, 2016. Reuters

The first tourists expected to journey to the Moon may be in for a bumpy ride. While the prospect of traveling in a SpaceX spaceship in 2018 is exciting, experts said the experience may involve constant vomiting as the body goes into a shock from the difference in gravity.

“Like every single astronaut who goes into space, they're going to get... very bad motion sickness,” the Centre for Altitude Space and Extreme Environment Medicine in London’s Daniel Grant told Agence France-Presse. Other symptoms would include getting claustrophobic, a constant need to pee and exposure to radiation.

Elon Musk’s SpaceX made the announcement Monday that it would send two volunteers—who have already deposited a significant amount of money for the trip—on a mission in 2018 that would travel around the moon.

"This presents an opportunity for humans to return to deep space for the first time in 45 years and they will travel faster and further into the solar system than any before them,” SpaceX said in a statement.

The mission is scheduled to loop around the moon, travel a little bit more into outer space before coming back and doing a loop to Earth. The distance traveled would equal roughly 400,000 miles, SpaceX’s CEO Elon Musk said in a teleconference.

Astronauts have previously cited difficulties with adjusting to outer space including Scott Kelly, who answered questions on a Reddit AMA. Getting sleep is particularly different because of how to position the body during bedtime.

“Sleeping here in space is harder than on a bed because the sleep position here is the same position throughout the day. You don't ever get that sense of gratifying relaxation here that you do on Earth after a long day at work. Yes, there are humming noises on station that affect my sleep, so I wear ear plugs,” Kelly wrote.