I have been diagnosed with sleep apnea. I have been using a c-pap machine for 2 mos. At follow up month 1, there was concern about shallow breathing showing up. Now at month 2 follow up, the shallow breathing episodes are worse. They want to monitor me for 1 more month, and if it shows that I am still struggeling with shallow breathing, they will send me home with something to hook me up to monitor my oxygen for 1 night. She also said that they may have to switch me from a c-pap machine to a bi-pap machine. What are some causes for shallow breathing?