This is described as a feeling of overall weakness, a feeling of discomfort, feeling like you have an illness, simply not feeling well. It often occurs with fatigue and an inability to restore a feeling of health through proper rest. Sometimes, it happens suddenly. Other times, it may develop gradually and persist for a long period. The reason behind it can be extremely difficult to determine because it can be the result of many conditions.

This is the scientific study of adverse effects that occur in living organisms due to chemicals. It involves observing and reporting symptoms that arise following exposure to toxic substances.

This is a large, dark-red gland located in the upper right portion of the abdomen, just beneath the diaphragm. Its manifold functions include storage and filtration of blood, secretion of bile, conversion of sugars into glycogen, synthesis and breakdown of fats and the temporary storage of fatty acids, and the synthesis of serum proteins.

This is inflammation of the tracheobronchial tree that occurs in patients without chronic lung disorders. The cause is almost always a viral infection. The pathogen is rarely identified. The common symptom is cough, with or without fever, and possibly sputum production. Diagnosis is based on clinical findings. Treatment is supportive; antibiotics are usually unnecessary. Prognosis is excellent.

This is an unpleasant sensation on the skin, provoking the desire to scratch or rub it. It is common in many types of skin disorders, especially allergic inflammation, and parasitic infestations.

Loose, watery and possibly more-frequent bowel movements are a common problem. This condition may be present alone or be associated with other symptoms, such as nausea, vomiting, abdominal pain or weight loss. Luckily, it is usually short-lived, lasting no more than a few days. But when it lasts beyond a few days into weeks, it usually indicates that there's another problem - such as irritable bowel syndrome or a more serious disorder, including persistent infection, celiac disease or inflammatory bowel disease.