When we look at chronic pain patients, there is abnormal electrical activity in pain pathways. Under normal conditions, there should be no spontaneous electrical activity. It is unclear why, for example, in patients who have strokes involving part of the pain system, pain develops three, six months, maybe a year after the stroke. We think that abnormal connections develop in pain pathways to produce this chronic pain. This may be the reason why injuries to the spinal cord, even many years ago, can still produce severe, chronic pain states.
Endorphins are naturally-occurring opioids.
In most settings, it's not clear that natural endorphins injected into a patient offer a significant advantage over synthetic things, such as morphine. The correlation is quite poor. The factors are very poorly understood. Talk about electronic blocking of pain. Something very simple, transcutaneous electrical nerve stimulation, is thought to work by eliciting events in the spinal cord that change the amplification of pain messages.