
Pain is defined as an unpleasant feeling brought on by a noxious stimuli or injury. The expression of pain can drive someone to stay away from harmful situations, defend injured tissues and avoid similar situations in future. Usually pain is classified as either acute or chronic, and can also be classified into mild, moderate and severe on the basis of severity of pain. The most common types of pain include back pain, orthopedic pain, cancer pain, post-surgical pain and neuropathic pain. Acute pain lasts for shorter duration and gradually resolves as the injured tissue heals but chronic pain lasts longer than 12 weeks and persists even after complete tissue healing.