By December 1914 as many as 10% of British officers and 4% of enlisted men were experiencing "nervous and mental shock".The term "shell shock" was coined during the Battle of Loos to reflect an assumed link between the symptoms and the effects of explosions from artillery shells. The term was first published in 1915 in an article in The Lancet by Charles Myers. Some 60–80% of shell shock cases displayed acute neurasthenia, while 10% displayed what would now be termed symptoms of conversion disorder, including mutism and fugue.The number of shell shock cases grew during 1915 and 1916 but it remained poorly understood medically and psychologically. Some physicians held the view that it was a result of hidden physical damage to the brain, with the shock waves from bursting shells creating a cerebral lesion that caused the symptoms and could potentially prove fatal. Another explanation was that shell shock resulted from poisoning by the carbon monoxide formed by explosions.At the same time, an alternative view developed describing shell shock as an emotional, rather than a physical, injury. Evidence for this point of view was provided by the fact that an increasing proportion of men with shell shock symptoms had not been exposed to artillery fire. Since the symptoms appeared in men who had no proximity to an exploding shell, the physical explanation was clearly unsatisfactory.In spite of this evidence, the British Army continued to try to differentiate those whose symptoms followed explosive exposure from others.
Chronic fatigue may refer to:

Fatigue (medical)#Chronic, a long-term state of physical or mental exhaustion, a symptom of many chronic illnesses
Chronic fatigue syndrome, a medical condition characterized by long-term fatigue and other long term symptoms that limit a persons ability to carry out ordinary daily activities.