Yes, Space Mountain at Magic Kingdom is notoriously bumpy and "jerky." Unlike modern "smooth" coasters like TRON Lightcycle / Run or Guardians of the Galaxy: Cosmic Rewind, Space Mountain is an older, classic "wild mouse" style coaster in the dark. It features sharp turns, sudden drops, and a rattling sensation that many riders find quite rough on their neck and back. The ride vehicles are single-file "rockets" that do not have significant padding, which amplifies the feeling of being tossed around. While the lack of light makes the ride feel faster than its actual top speed of 28 mph, the structural "rickety" feel is a core part of its thrill for some, while others find it physically uncomfortable. If you are prone to motion sickness or have pre-existing back or neck issues, you may want to skip this one or prepare for a bit of a "brawl" with the tracks in the dark.