Between factors like restless nights of sleep on board and unhealthy in-transit eating habits, many fliers are fatigued and unhealthy when travelling.

BBC: Sleep in a pod on the fly

Among the conditions examined by the St Thomas' team were obstructive sleep apnoea (OSA) and restless leg syndrome (RLS).

BBC: NEWS | Health | Genes to blame for restless sleep

The troops are tired because they were anticipating the order to go and even though you try to sleep, usually, it's very restless, as you can imagine.

CNN: Grange: Troops 'on a high'

According to the American Academy of Sleep Medicine, there are 81 chronic sleeping disorders, from apnea, which causes interrupted breathing, to restless leg syndrome.

FORBES: Who's making big bucks off your insomnia?