What is Pain?
This is a very in depth topic, but for the sake of simplicity, acute pain is primarily the perception of a special sense called nocicpetion and chronic pain is a result of a maladapted nervous system.
Acute Pain & Nociception
Nociception is a consequence of tissue damage or inflammatory changes. So, if you are feeling pain there must be tissue damage (injury, malfunction or inflammation). The cause of your pain can usually be identified by a chiropractor or medical doctor via a thorough examination and diagnostics (X-Rays, Labs, etc).
Chronic pain is different. In chronic pain, there need not be active nociception. After a period of time our nervous system can become maladapted and begin to interpret normal stimuli as pain. This may occur secondary to an injury / episode of acute pain, long term inflammatory conditions, chronic strain, etc. Chronic pain must be treated differently with a focus on whole person support, active treatments, and cognitive behavioral approaches.