Vagitonin
When after sexual intercourse (he) is hit by a wave of immense relaxation and tiredness brought fourth by being completely satisfied from being deep in (she) vagina, comparable to the sleepiness one experiences when taking Melatonin.
Man: "Damn, my girl hit me with that Vagitonin last night, I slept through all twelve of my alarms, the eviction notice being nailed to the door, a shooting at my apartments and just woke up (@5pm)"