When you go get a DOT physical, you fill out the long form, checking off all the boxes indicating symptoms and diseases you have (or have had), and space is provided to detail some of them with dates, treatments received, and any current limitations.
If you check the box YES next to Shortness of Breath, Lung Disease, or especially next to Sleeping Disorders, you should expect some followup questions regarding your pulmonary health. You'll be asked if you have Excessive Daytime Sleepiness, if you're tired or sleepy during the day, if you wake up a lot during the night, if you snore. If you answer yes to any of those, the doctor can disqualify you if he feels you have a pulmonary problem that can affect you safely driving a CMV. He can also recommend that you have a sleep test if he thinks you have sleep apnea, and can disqualify you until you complete the test. This is nothing new.
What's new is the fact that the FMCSA Medical Review Board has put into the Guidelines for Examiners the bit about looking for reasons to order sleep tests, and recommending them for any and every little thing, including things that aren't even in the Regulations. Not coincidentally, the FMCSA Medical Review Board is comprised chiefly of doctors who work in the sleep disorder business, they're primary income is derived from the treatment of sleep disorders and the sale of CPAP machines. FMCSA Certified physicians get a referral fee (otherwise known as a kickback) for each sleep study they order. The new training materials for FMCSA certification is written as if the sleep apnea study is a part of the FMCSA Regulations. But it's not. It's the same as it's always been, where if you have a legitimate pulmonary problem that needs to be addressed, the doctor can order the study.
OK, here's where doctor shopping comes into play. If you checked those YES boxes and the followup questions indicate you need a sleep study, and you are disqualified because of those checked boxes and the answers to the questions, and you decide to get a second opinion, then you had better make absolutely certain that you check the same YES boxes and answer the followup questions the same way with the second doctor. The two Long Forms will be compared. If the second doctor passes you based on the same information you gave to the first doctor, you're good to go.
However, if you answer NO next to those boxes with the second doctor, and you get passed, you're probably gonna lose your CDL over it. That's doctor shopping.
It's the same with other potentially disqualifying diagnosis, like diabetes, or cardiovascular problems like angina. If you've been diagnosed with those, and you check YES to it on the long form and are disqualified, but go to a second doctor and check NO to it, you're gonna get in trouble. But if you check YES at the second doctor and get passed, that's simply a second opinion (on the same information) and there's nothing wrong with that.
A DOT Medical Examiner will not diagnose you with sleep apnea, diabetes or anything else. He'll refer you to a physician for testing and diagnosis treatment.