Fatigue that is worsened by pain can affect motivation and mood. It can even cause physical symptoms such as heavy, achy limbs. Of course, not everyone will experience such severe fatigue due to pain; however, fatigue and chronic pain are closely connected nonetheless. There are a few reasons, in particular, that may cause pain to contribute to fatigue. Pain affects sleep Pain is exhausting Pain can be connected to inflammation Pain medication can cause side effects Pain can reduce activity levels