It is necessary to mention it. My impression is, the best way to go is to get the apnea treated first, most likely with CPAP. Once your sleep is improved and you get more energy, then you should get on a weight loss program, using diet and exercise. After losing weight, it's possible you won't even need CPAP anymore, and you'll be "cured" from apnea.

This is why losing weight is one of the most important steps. The CPAP should make it easier to do so.