http://www.sleepapnea.org/info/index.html
as many as 12 millions in the US alone..
excerpt from bove link
Sleep apnea is very common, as common as adult diabetes, and affects more than twelve million Americans, according to the National Institutes of Health. Risk factors include being male, overweight, and over the age of forty, but sleep apnea can strike anyone at any age, even children. Yet still because of the lack of awareness by the public and healthcare professionals, the vast majority remain undiagnosed and therefore untreated, despite the fact that this serious disorder can have significant consequences.
It wakes me up once a night. I have to gasp once for breath. It's the pits.