Every single person I know who has been through a sleep study was diagnosed with sleep apnea. EVERY SINGLE ONE. Then they have to get fitted for a CPAP and then they (or their insurance) has to pay for the CPAP. I'm not saying they don't all have sleep apnea, but I will point out that, according to Forbes:

"In 2010 there were 2,280 sleep labs in the U.S. generating around $5.9 billion. This year [2015], 2,800 labs are set to haul in an estimated $7.1. billion. By 2020 the industry will be within eyeshot of the $10 billion mark."