References to pain exists since the time of Homer, who wrote about it in the 8th century BC. Hippocrates described pain in more detail in the 5th century BC. The father of medicine said that "Everything that changes in relation to its nature and destroyed, results in pain." Hippocrates believed in the theory of the opposites for treating pain, i.e. for example, a subject naturally warm, being ill due to cold, will be cured by hot. The theories of Hippocrates gradually spread from Greece to the known world of the time. Progressively, the knowledge about pain, its causes and treatment developed over the centuries and with the development of medicine and the available assessment tools, we now understand much more about it. In recent decades the work of Professor Melzack has been very important. He referred to the gate pain control theory in 1965  and the theory of neuromatrix in 1996 . Today, we know about the importance of brain processing and understanding of the messages that come from the periphery and the brain's ability to create responses to these messages (e.g. hand removal movement when it is burned in the fire). Melzack says that many factors contribute to the creation of pain, including cortisol, gender related hormones, genetic predisposing factors and psychological pressures [2,3,4].
The definition of pain
The International Association for the Study of Pain (IASP) defines pain as "an unpleasant sensory and emotional experience, combined with actual or potential tissue damage or described in terms of such damage" . By definition, it is understood that pain is a personal reality for the one who feels and describes it. Pain is a subjective phenomenon so that each person can feel and describe it differently. The forms of pain can be both aesthetic and emotional. Based on the above definition, pain may be due to both actual and possible tissue damage. To better understand the last sentence it is important to understand the difference between acute and chronic pain.
Acute and chronic pain
Acute pain is the warning of the body that something has happened to it, such as an injury. So, it is a normal reaction that aims to protect the organization and lasts until the injury is healed. This healing period, usually lasts up to three months and then acute pain goes away. Chronic pain is pain that lasts for more than three months, although some scholars believe that this time should be more than six months.
Chronic pain may be continuous or intermittent. It may be the result of a known cause, such as an injury or a disease, but it can be of unknown aetiology. Often, the cause of chronic pain has passed, but the body still sends alarm signals. When pain persists, you may feel that it destroys your life and it does not offer you anything . However, even a chronic "bad" pain indicates that the brain for some reason concludes that there is a risk . In the case of chronic pain the distress signal sent does not mean that the body is directly threatened and that there is "risk", but it means that there is a problem in the processing of pain. The important thing is to find the cause that makes the brain believe that there is a problem,  that is, where the mistake in the processing of pain is. The presence of chronic pain is not normally an experience that creates disability, but often the reactions to the presence of chronic pain can contribute the the creation of disability . Such a reaction is often the feeling of catastrophizing leading to avoiding activities. Over time, avoiding activities and the disability that causes, lead to the reductions of pain resistance level, thus experiencing more pain .
Pain in Chronic Fatigue Syndrome and quality of life
It is understood that the experience of pain reduces the person's quality of life, it may limit their going out and lead to isolation and in some cases depression. Pain often not only affects the person who has it, but also their friends and family.
Chronic Fatigue Syndrome (CFS) is often accompanied by joints and muscles pain and headaches . Pain symptoms can occur in over 90% of people with CFS . A study has shown that people with CFS have lower resistance to pain levels than healthy subjects . Another study showed that in CFS there is the feeling of catastrophizing and depression, affecting the appearance of pain .
For the treatment of pain in CFS it is particularly important that the patient understands the biopsychosocial model of its appearance. This can be done by training the patient . Research has shown that training about the physiology of pain in individuals with CFS reduced catastrophizing and as a result the existence of pain . Pain felt by a person with CFS may increase after exercise. It is thus, very important that the therapist advises the correct exercise dosage, which will not increase the symptoms of fatigue and pain. For this reason, the therapist MUST be a specialist in Graded Exercise Therapy in CFS or chronic fatigue due to other causes. This is what is recommended by the National Institute for Health and Care Excellence of the United Kingdom .
In the program of Graded Exercise Therapypain management is of importance. The administration of the correct dose and type of exercises, without causing extra pain symptoms, is a condition to improve the patient's situation. The training, the specialisation and the years of clinical experience of Dr Michailidou in using Graded Exercise Therapy in Chronic Fatigue Syndrome and chronic fatigue in general, are important factors in order to effectively help people with these disorders.