ABSTRACT
Pain is the most common symptom for which patients seek medical attention. According to the International Association for the Study of Pain (IASP), pain is defined as an unpleasant sensory and emotional experience associated with actual or potential tissue damage or described in terms of such damage [1]. Pain is always subjective. The subject may experience pain regardless of actual existence of any stimuli, and inability to communicate the pain does not mean that it does not exist. The cause of pain may be underlying disease, injury, surgery, or simply unknown. Pain can be categorized based on its duration as well as mechanisms.
