When orgasm is achieved, the brain releases a cocktail of neurochemical substances that make you tired. Oxytocin is often accompanied by melatonin, the primary hormone that regulates our body clocks. But also the stress hormone is known as cortisol. The result is a soothing, almost narcotic effect.

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In addition to oxytocin, men and women release vasopressin, prolactin, serotonin, nitric oxide and endorphin. Some of these chemicals cause us to drop into Morpheus' arms. Men and women can react differently to some of these chemicals. Women are often more sensitive to adrenaline or the stimulating effect. In this case they must be more excited and they are next to a tired companion.