Pain and insomnia
Pain and insomnia is a fairly common condition, particularly with the elderly. The relationship between the two is bi-directional, meaning that one impacts on the other, i.e., pain will cause insomnia and insomnia will reduce the threshold to pain. Because this bi-directional relationship is so influential, it is often considered that the benefits of breaking the cycle, e.g., by using sedatives or pain killers, outweigh the risks, e.g., overdose, addiction.
The exact reasons why pain causes insomnia are not completely understood, however, it seems that pain in the body creates conditions which increase signaling activity through the nervous system to the spine and brain, that prevent relaxation and increase states of being awake, e.g., by increasing cortisol levels.
More recently it has come to be understood that when treating insomnia caused by pain, cognitive and behavioral practices that focus on relaxation can be highly beneficial, including having longer lasting effects than treatments involving medication.