The purposes of this study are to first learn whether persons with insomnia do have a misaligned sleep system compared to persons who do not have insomnia by assessing the sleep of people before and after a period of extended sleep loss. Second, the study will determine whether cognitive-behavioral therapy can re-regulate the sleep system and its response to sleep loss. Third, the final purpose is to examine whether the immune system of people with insomnia is more altered following sleep loss than in the comparison group and whether cognitive-behavioral therapy can alter immune function.