Chronic pain and sleep disorders are independently associated with a reduction in the quality of life. They can be both a cause and consequence of each other; therefore, they should be treated simultaneously. However, optimal treatments for chronic pain-related sleep disorders are not well established. Here, we aimed to investigate the effects of suvorexant, a novel sleep drug, and mirtazapine, a noradrenergic and specific serotonergic antidepressant, on pain-related sleep disorders in a preclinical neuropathic pain mouse model, which was produced by partial sciatic nerve ligation. We calculated the quantity, duration, and depth of sleep by analyzing the electroencephalogram. Voluntary activity was also evaluated by counting the number of wheel rotations with special cages. Daily administration of suvorexant and mirtazapine normalized the reduced rapid eye movement (REM) and non-REM sleep and improved the fragmented sleep, further regaining the depth of sleep at sleep onset in the chronic pain state. Suvorexant decreased voluntary activity, which was prolonged after the end of administration; however, mirtazapine did not decrease it. Both suvorexant and mirtazapine could be potential therapeutic agents for chronic pain-related sleep disorders.