BACKGROUND: Motion sickness remains a significant and unpredictable problem during spaceflight. One of the major difficulties in understanding the etiology of space motion sickness has been a lack of data at the time the symptoms occur, i.e., immediately after entry into space and during return to Earth; in these phases of the mission is when critical operational tasks are performed.CASE REPORT: We report here the case of a crewmember who experienced severe motion sickness symptoms immediately after launching into space and for several days into the mission. Verbal reports recorded during and immediately after the flight describe in detail the symptoms and their underlying causes. The prominent cause was oscillopsia that was induced by moving the head, wearing prescription eyeglasses, and translating the whole body.DISCUSSION: In this case, space motion sickness was sudden and induced by voluntary or involuntary head or body movements in any plane. These head movements caused a visual disturbance that induced the perception that the environment was oscillating. The exaggerated motion perceptions suggest an increased vestibular sensitivity and/or decreased pursuit-optokinetic mechanisms in orbit and immediately after landing.Reschke MF, Wood SJ, Clément GR. A case study of severe space motion sickness. Aerosp Med Hum Perform. 2018; 89(8):749–753.