When you sleep well (especially relating to the proper times of sleep) your body produces an abundant supply of melatonin. More and more we see how melatonin impacts both the eggs and sperm:
“Melatonin could become an important medication for improving ovarian function and oocyte quality, and open new opportunities for the management of several ovarian diseases.” From Tamura and Colleagues (2009) Melatonin and the ovary: physiological and pathophysiological implications, in Fertility & Sterility. Link here.
“There were statistically significant improvements in post‐operative parameters of semen analyses (sperm concentration, motility and proportions of normally formed spermatozoa), peripheral blood inhibin B and total antioxidant capacity in melatonin group compared with placebo group. In conclusion, melatonin therapy adds extra benefit to varicecelectomy in terms of sperm parameters, peripheral blood inhibin B and total antioxidant capacity” From Lu and Colleagues (2018) Melatonin therapy adds extra benefit to varicecelectomy in terms of sperm parameters, hormonal profile and total antioxidant capacity: A placebo‐controlled, double‐blind trial, in Andrologia. Link here.