Nodding off after dinner or wanting to sleep till noon could indicate circadian rhythm disorders.

WSJ: Unraveling the Riddle of Too Much Sleep

Moreover, constantly changing patterns is disastrous for the body as the circadian rhythm is "completely shot", says Professor Skene.

BBC: RELATED BBC SITES

Past research has linked the graveyard shift to certain health issues, in part because it disrupts our circadian rhythm and shifts body chemistry.

FORBES: Environmental Risks For Breast Cancer: What You Need To Know

"Exercise is known to help with sleep if you don't do it just before bedtime, " possibly because it promotes overall good health and helps enhance the body's circadian rhythm, which promotes activity during the day and resting at night, says Rapoport.

CNN: Exercise plus sleep may lower cancer risk in women