u could try turkey
the real stuff from a oven craved at home turkey ..........someone will know the chemical name i can say it but not even going to try to spell it

turkey sandwitch about 2 hours before i want to sleep i am happy camper

and as for only some times ..........go freaky get that chemical release in the brain and pass out might take 2 3 times around but soon or later body will flip that ahhhh we good switch and sleepy time comes along .........the down side to this after so many times the amount to trip sleepy effect well put it this way your a porn star