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A 54-year-old woman developed vertical oscillopsia over 24–48 hours, with gait unsteadiness; both of which persisted. Two months after onset, she reported isolated 5–10 min episodes of ‘flying in a cloud’ with spatial disorientation, even in familiar places. On examination 3 months after symptom onset, she was alert but her gait was unsteady. Attempted sustained upgaze induced vertical diplopia with small-amplitude horizontal saccadic intrusions ( figure 1A; online supplemental video 1, first segment). Forced horizontal gaze elicited subtle torsional oscillations (online supplemental video 1, second segment). When supine with her eyes closed, tactile or gentle percussive stimulation triggered a brief trunk- and proximal limb-predominant startle-like response (figure 1B; online supplemental video 1, later segment). Her mini-mental state examination score was 27/30, and neuropsychological testing showed global slowing and anterograde memory retrieval deficits. MR scan of brain showed bilateral mesial temporal T2-FLAIR hyperintensities without contrast enhancement but no visible brainstem lesion (see figure 2).