Hypothyroidism Hyperthyroidism Malignancy Rheumatoid arthritis, systemic lupus erythematosus, polymyositis, Sjogren syndrome, psoriasis arthritis Crohn’s disease, ulcerative colitis, coeliac disease Post-concussion syndrome, post-ICU syndrome, post-traumatic stress disorder Heart disease, such as heart failure Severe chronic obstructive pulmonary disease, other severe respiratory diseases Severe anaemia, vitamin B12 deficiency, haemochromatosis Renal failure Diabetes mellitus Addison’s or Cushing’s disease, hyperparathyroidism, and other endocrine disorders Bipolar disorder, schizophrenia, major depression, anorexia, bulimia, autism Multiple sclerosis, myasthenia gravis, other neuroimmunological diseases, paraneoplastic syndromes Parkinson’s disease, Alzheimer’s disease, stroke, other serious neurodegenerative diseases Sleep apnoea Narcolepsy Hepatitis, tuberculosis, HIV/AIDS, neuroborreliosis, other chronic infections Excessive consumption/abuse of alcohol or other substances