Great questions. Sadly, we do not have specific answers to any of them.
I suspect that we will discover some people inherit genes that make them likely to develop sleep apnea. But just as you can avoid diseases such as type 2 diabetes and coronary artery disease by making healthy lifestyle choices early in life, we may find ways to avoid sleep apnea.
Take body size as an example. Obese people have a higher risk of developing apnea compared to people that are not overweight. Yet, many thin people who are fit have sleep apnea and some extremely obese people don't.
The most common symptoms of sleep apnea are loud snoring, poor sleep quality and excessive sleepiness during the day. Although you might not be able to completely relieve these symptoms without specific therapy, the following can help:
- Lose weight if needed
- Become more physically active
Do at least 30 minutes of aerobic exercise most days of the week
- Limit alcohol consumption
This mean no more than one drink per day for women and two drinks per day for men. You might also try stopping all alcohol consumption to see if it helps.
Although not proven, it seems quite reasonable that stress and extreme fatigue would make the symptoms of sleep apnea worse. But I doubt these factors alone would be the actual cause.