Pain is very complicated in that it may trigger a process called sensitization. When one body part is having persistent pain, our brain as well as the nerves in that area will gradually become more and more sensitive to the pain signals, meaning that pain threshold will gradually reduce. Many things fasten up the sensitization process, such as inflammation, poor sleep, stress, anxiety and depression. So if we take poor Uncle Tan for example again, he is having a lot of pain and a lot of inflammation that he could not fall asleep. And uncle Tan may be running his own shop. He will not be able to work for several weeks due to the injury, and there is no one else to help him take care of the shop. He is worried about the loss of income, and all the rentals and bills that he still have to pay. The lack of sleep and profound worries make his system more and more sensitive to pain, thus he will feel more intensive pain, and even worse sleeping quality, and even more worries about the condition. Everything spirals into a vicious cycle.