Answer: biorhythms

AnswerCrossword Clue
biorhythmsA recurring cycle in the physiology or functioning of an organism, such as the daily cycle of sleeping and waking
biorhythmsA cyclic pattern of physical, emotional, or mental activity said to occur in the life of a person
biorhythmsBIORHYTHM, a periodic change in the behaviour or physiology of many animals and plants (eg hibernation and migration) mediated by hormones which are in turn influenced by changes in day-length