If you're saying you've been diagnosed with chronic sleep apnoea which is affecting your ability to concentrate and stay awake at the wheel then that will be of concern, like any other medical condition that affects your ability to drive.

Don't know where you are, but here in WA the application for a drivers licence specifically asks about such conditions - see below, and I'd assume it would be similar in all other states.

However, I don't think the use of a CPAP machine in itself would simply disqualify you from driving, after all it means your sleep apnoea is being treated and therefore your symptoms are being contained, like wearing prescription glasses to drive, is it not?

So, I would advise you put "sleep apnoea" under medical conditions on the application, and put the fact you are using a CPAP machine in the section about treatment below that, and see if they require any further medical examination or evidence as to your fitness to drive. One such piece of evidence could be if you do another sleep study with you using the CPAP machine, and then you'd have medical proof whether your CPAP machine is containing your symptoms or not. I have that, a before and after sleep study which attests to the effectiveness of my CPAP machine in containing my symptoms. Another piece of evidence is to show you have been "taking your medicine" as it were. My CPAP beams a daily log of it's use via a built-in SIM card to ResMed, the manufacturer, so they could presumable provide a record of the CPAP being regularly used if required to do so. I know this because I stopped using mine for a few weeks and I got a polite email from them noting the fact and asking if there was anything they could do to help! The usage data is also recorded on the removeable SD card so could also be provided as proof of use if ever required. The flip side to this is however, is that it will also show if you haven't been using it!

Should you fail to inform the department of transport about your condition, and you are involved in an accident due to lack of attention or falling asleep at the wheel, I would imagine the legal and insurance consequences could be dire if they subsequently uncover your medical records.

I should stress that all this is just my personal opinion, I am not a doctor or lawyer, nor do I work for the department of transport!