Thanks for posting on HCM,
is a way of protecting their selves and their colony and the substance/toxin that is injected into the human tissue is aimed both to irritate and cause pain. Normally a single sting should not make you feel sleepy, but several stings can be very dangerous and since you receive serious doses of the toxin, it can cause you to feel sleepy and if more doses, it can cause death. Bee sting allergy
is possible and fatal too. I recommend you do not make it a hobby for bees to sting you and avoid getting more of the toxins. You might develop immunity against the toxins if continual low doses hence the reason why you no longer feeling a lot pains after the sting.
Well hope this helps