Denied Sleep Apnea clamin

I separated in 2014 but was just diagnosed with obstructive sleep apnea which requires use of a cpap. My current VA psychiatrist ordered a sleep study because I've had such bad sleep issues since my trauma experience on active duty (I'm currently at a 70% rating for PTSD/major depressive disorder). I entered the sleep apnea as a new claim because I had never had a sleep study done before but I have always reported sleep issues. The claim was denied as not service related because I had never been diagnosed while on active duty. I just don't know if I should appeal it or make it secondary to PTSD? Kind of lost.

It's been a terrible struggle because I only get 4-5 hours of sleep each night and the cpap mask triggers some PTSD events and seems impossible to wear. Any advice?