How to file a VA sleep apnea claim (canonical PTSD secondary, 50% CPAP)

5-step Schema.org HowTo for sleep apnea — completes acoustic-trauma + PTSD secondary cascade. CPAP-dependent rated 50% (38 CFR 4.97 DC 6847). 3 SC pathways: direct in-service onset; secondary to PTSD (Krakow et al. literature); secondary to other SC (TBI, GERD, sinusitis, medication-induced weight gain). Sleep study (polysomnogram/HSAT/civilian), nexus opinion ("at least as likely as not" 38 CFR 3.102), CPAP usage data submission for 50% rating.