For sleep apnea you may look into playing the didgeridoo for 30 minutes a day. The circular breathing every day really improve people's symptoms, and I've heard you see results after a few weeks or months. I'm in the middle of trying this but unfortunately I just haven't been doing it every day.
I've also heard just practicing circular breathing by blowing through a straw into a cup of water can produce the same effect but playing a didge is just so much cooler.
I haven't read into it much but I believe the circular breathing excercises strengthen some of the muscles that tend to relax during sleep so they keep your airway open.
I've also heard just practicing circular breathing by blowing through a straw into a cup of water can produce the same effect but playing a didge is just so much cooler.