Hello - I just found this string and wanted to mention I have experienced the weird involuntary exhale scenario twice. The first time was after hip replacement about 10 years ago and the second time is now, after the 2nd hip replacement. For me it only happens when I am resting in bed (middle of the night). It was happening quite a bit last night so I thought I would try and video it (lips moving involuntarily to expel air). But nope. Apparently just tensing my hand/arm to hold the phone stopped the involuntary exhales. Once I put the phone down and rested again it started up again. I am also taking opioids at night to help me sleep which is course depresses the breathing. So, I'm thinking, a surgical event, opioid use and deep relaxation brings on the involuntary exhales for me. Once I completely recovered from surgery the first time the involuntary exhales stopped. They didn't hurt. Just an annoyance.