I just did a quick google search on something like sleep apnea without snoring and the articles that popped up indicated it is possible. I really encourage you to pursue this. As a first step, he can do a simple overnight study at your home with a finger monitor. If the results indicate he has sleep apnea, he can follow up with an overnight study at a sleep center. There they identify specific issues and the type of machine (CPAP, BIPAP, or vin with or without oxygen) and prescription for that machine that will help him get restorative sleep. It's worth a shot!