The reasons why cancer usually hurts at night can be explained in two ways: 1. Attention is shifted. During the daytime, patients receive more information from their senses such as hearing and vision, so their attention is shifted, which makes them feel less pain and even less pain. At night, the information received by eyes and ears is obviously reduced, and the attention is focused on pain, so the pain is obviously increased. 2. Cancer pain is usually transmitted by parasympathetic nerves. During daytime, sympathetic nerve excitability is dominant and parasympathetic nerve impulses are suppressed, so patients feel no pain or light pain, but at night, parasympathetic nerve excitability increases, which makes patients feel more pain.