Circadian rhythm - refers to any biological process that displays an endogenous, entrainable oscillation of about 24 hours. These rhythms are driven by a circadian clock, and rhythms have been widely observed in plants, animals, fungi and cyanobacteria. The term circadian comes from the Latin circa, meaning "around" (or "approximately"), and diem or dies, meaning "day".
Signs That You Have a Circadian Rhythm Sleep Disorder
Delayed sleep phase disorder (DSPD), officially called circadian rhythm sleep disorder, delayed sleep phase type, is an inability to fall asleep at a desired, conventional clock time and awaken at a socially acceptable morning time.
Go to sleep too late and wake up too late? Having a delayed sleep pattern could be 'Delayed Sleep Phase Syndrome' (DSPS). DSPS is believed to be a disorder of the body's internal clock - the circadian rhythm. DSPS sufferers have difficulty falling asleep and waking as their circadian rhythm is out of sync with regular sleeping and waking times i.e. sleeping at night and waking in the morning. This sleep infographic has more information.