Pain is unpleasant
Pain is an unpleasant sensation. Pain is of many types and it indicates that we are hurt. Pain is a sensory experience that can be caused by many different kinds of injuries. It is also an emotional experience that causes discomfort or distress or agony, which haunts us and disturbs our day-to-day activities.
Pain is a defense mechanism
Pain is, in fact, a defense mechanism of the body, by which it alerts the organism regarding the tissue damage. It is almost always accompanied by healing and tissue repair. And, when the pain goes away it tells us that the repair process has been completed. But, pain can also last well beyond the point of tissue repair (spinal cord injury pain) or appear without tissue damage (migraine headaches, low back pain) or be felt by stimuli that do not normally evoke pain, like lightly touching the skin (post shingles pain, diabetic nerve damage pain). So, there is much more to pain than a simple sensory process.
Chronic pain is a disease
Chronic pain is a disease in its own right. It is a state of pathological pain sensitivity. It lasts beyond the reasonable healing time of the original injury, worsens over time, and takes on a puzzling life of its own. There is increasing evidence that untreated pain rewires the central nervous system, causes pathological changes to the brain and spinal cord, and in turn causes greater pain. Moreover, prolonged pain also changes certain parts of the brain, including those involved in cognition. Treating pain as a problem, and not as a side effect of an illness, is something that is relatively recent.