There are many different levels of Pain. There is acute pain (sharp and intense) likely to be short-term and disappear within a few hours or days. Then you have Chronic pain (always there, persistent, drive-you-mad kind of pain) which can last for months or years.
Chronic pain can be anywhere in your body and for a number of reasons, however it doesn’t matter which type of pain you are experiencing, pain is not the problem. It is only the symptom.
If the cause of pain continues long enough, it will affect your Craniosacral System.1 Your body is now stressed further by trying to compensate to overcome the cause. This becomes increasingly difficult to ignore and causes other dysfunction within your body creating a cyclical state of mental stress and physical stress.
It's interesting to note that Biodynamic Craniosacral Therapy appears to work very well with clients who have had sciatica and not found relief via other methods.
Also refer to Back Pain
1Clinical research and observations have shown that dysfunction of the Craniosacral System can manifest into a variety of symptoms and degenerative processes.