In 1862, James Glaisher and Henry Coxwell ascended to 29,000 feet in an open hot-air balloon. During the ascent, Glaisher described marked neurologic compromises: appendicular and later truncal paralysis, blindness, initially preserved cognition, and subsequent loss of consciousness. The author examines Glaisher's account of balloon sickness by comparing it with other balloonists' observations and discussing it in the context of altitude sickness, decompression injury, and hypoxemia.