- https://www.sleepfoundation.org/how-sleep-works/why-do-we-need-sleep
- https://www.nhlbi.nih.gov/health-topics/sleep-deprivation-and-deficiency
- https://www.sleepfoundation.org/circadian-rhythm
- https://www.hopkinsmedicine.org/health/wellness-and-prevention/melatonin-for-sleep-does-it-work
- https://www.sleepfoundation.org/melatonin
- https://en.wikipedia.org/wiki/Suprachiasmatic_nucleus
- https://n.neurology.org/content/71/8/594
- https://www.yourhormones.info/hormones/melatonin/
- https://en.wikipedia.org/wiki/Enterochromaffin_cell
- https://en.wikipedia.org/wiki/Enteric_nervous_system
- https://en.wikipedia.org/wiki/Serotonin
- https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6005194/
- https://www.ncbi.nlm.nih.gov/books/NBK550972/
- https://www.sleepfoundation.org/sleep-disorders
- https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5353813/
- https://www.racgp.org.au/afp/200905/200905beach.pdf
- https://en.wikipedia.org/wiki/Insomnia
- https://pubmed.ncbi.nlm.nih.gov/26844312/
- https://www.webmd.com/sleep-disorders/insomnia-symptoms-and-causes
- https://www.mayoclinic.org/diseases-conditions/insomnia/diagnosis-treatment/drc-20355173