Loud noises. Whether flight attendants make mid-flight announcements, turbulence causes a seat back tray to rattle, or a baby cries somewhere in the cabin, sudden loud noises are, unsurprisingly, not conducive to restful sleep, and even anticipating more sounds can be a distraction.

Difficulty sleeping on a plane is the result of both physiological and environmental factors. Physiologically, your circadian rhythm is disrupted by changing time zones and artificial cabin lighting, which suppresses melatonin production. The cabin environment itself is hostile to rest: humidity levels often drop below 10%, causing dehydration and nasal discomfort, while the lower oxygen levels (equivalent to an altitude of 6,000–8,000 feet) can leave you feeling fatigued but restless. Environmentally, the human body is not biologically programmed to sleep in an upright position; the lack of neck support causes the head to "bob," interrupting the deeper stages of REM sleep. Combined with ambient engine noise, cabin announcements, and the vibrations of the aircraft, your brain remains in a state of "low-level alert," preventing the restorative sleep you would get in a bed.