There are three elements to proving your service connection for sleep apnea. First, you need a sleep apnea diagnosis from a medical professional and a recent sleep study (within the past 12 months). Second, you must show that your sleep apnea either started or worsened while in active duty service (this does not require a diagnosis during your time in service). Lastly, you need to connect your current diagnosis and the event during service that lead to your sleep apnea. Many veterans use nexus letters from a qualified medical professional to provide the link between diagnosis and service.