Circadian Rhythm Sleep Disorders Make an Appointment Find a Doctor Ask a Question Reviewed by Sheila Tsai, MD (March 01, 2017) Circadian rhythm sleep disorders are disorders of the timing of sleep and wakefulness. We all have an internal "clock." This "clock" controls our rhythm of sleeping and wakefulness. There are times of the day when we are most alert. This is often mid-morning and early evening. And, there are times when we are more likely to be sleepy — during early to mid-afternoon and late evening. Our environment has an impact on the timing of sleep and wakefulness, and may either complement or disrupt our internal clock. Associated Conditions Excessive sleepiness can develop when our sleep rhythm is altered. We may want to sleep during times when we need to remain awake. On the other hand, insomnia occurs when we attempt to sleep at a time when our rhythm wants us to stay awake. Programs & Services Sleep Center Clinical Trials For more than 100 years, National Jewish Health has been committed to finding new treatments and cures for diseases. Search our clinical trials.