Does sleep apnea go away by itself?

Depends on cause: "by itself" is the important part of the question -- there are modifications that can be made to reduce risk and occurrence. Weight loss is an example. In many cases, the obstruction of the airway requires treatment such as cpap, surgery, or other treatment and the problem will not go away by itself. Discuss further with your physician for your individual situation.

Possibility: Sleep apnea in general due blockage of the upper airway, either do to narrowing of the upper airway due to obesity or some anatomical problems like overbite or underbite, the main reason probably after age of 40 due to weakness of the upper airway muscles due to aging process. If you are 30 years and overweight, weight loss will help especially with mild case of sleep apnea.Also try throat excer.