Well, that is a bit of an exageration. It only falls out when I cough, so far as I know, but apparently I may cough more often than I realize. Not every night, but maybe 3 or 4 nights each week I find the filter has fallen out over night.
I use a ResMed Mirage Quatro mask and PR System One "brick" with the foam filter that you just shove into the air intake and resistance is supposed to hold it in place. I thought about using some tape to hold it in, but I don't want to add too much air flow restriction.
Is this a common problem or am I just a heavy breather?