Sept 21st is the next Full Moon and Oct 20th is one after.
Ever heard of the terms Lunatic? Lunar module? Lunar eclipse? On a full moon day the lunar effect is very high. If you go to the beach regularly then you will notice that the waves are trying to catch the sky "sort of speaking" on Full Moon days and near Full Moon days, than other days. Waves rise very high on Full Moon days, Like Newton's theory "every thing goes up, must come down to earth" the moon too has it's own magnetic power of pulling things towards it.
It is said that the brain waves of the mentally retarded are pulled towards the Moon "sort of speaking". Hence they act more crazier on Full Moon days and are called lunatics.
Hospitals report more deaths on Full Moon days.
If you had a cut or an injury due to an accident on Full Moon days, you tend to bleed severely or incur more pain. Any sicknesses, one may have tend to take an adverse effect on Full Moon days.
Those who goes through the monthly cycle may have noticed that their "periods" are severe or painful, on or closer to Full Moon days.
So it is rational to think that the Gallbladder flushes more stones or perhaps gives us more pain on or closer to Full Moon days.
It is the holiest day for Buddhists, as Buddha was born on a Full Moon day and he attained Nirvana on a Full Moon day!