There are a large number of options available for use of a C-Pap or BiPap respirator in a Lazy Daze. Varying LD models have 12 volt and 120 volt outlets in varying locations. Which you use, and how you use it, will depend on your respirator, its power requirements, where you sleep and your model of RV. A respirator usually will not require a great deal of power. Most Lazy Daze units have sufficient battery power to operate a modern high efficiency respirator overnight.
Use of a heated hydration system or use of an older, less efficient model may require additional power.
Some people require the addition of oxygen to generate higher partial pressures of oxygen in the air delivered by their respirator. This typically requires the use of an oxygen concentration device. Such will draw far more than a simple CPAP or BiPap machine. Even if you use a cylinder rather than a machine to obtain oxygen, the interior of an RV is NOT a spark-free environment. The use of oxygen in an RV is way beyond the scope of this discussion.
If you plan to boondock or dry camp (camping without depending on external hookups), and you have not yet bought your respirator, a unit that runs on 12v DC power with a cigarette lighter type power cord and no converter or inverter is probably a good choice if available. Units designed for 12v use seem to draw less power than units designed for 120v, which use an inverter to step the 12v power up to 120v. Look at the voltage and amperage of your respirator to determine your power needs. My unit is 12 volts, 3 amps, for 36 watts. Battery capability is typically in amp-hours. At a 3 amp flow, 9 hours of use overnight consumes about 27 amp-hours for me, an amount that can readily be accommodated in most LD's. If you plan to be up much of the evening, with multiple lights on, in cold weather with your furnace running and your TV on, with no shore power connection, you might be asking a bit too much from a two battery system. The respirator is not likely to be the straw breaking the proverbial camel's back in such a case, but if you are dependent on a respirator, you don't want it quitting in the middle of the night on you.
The simple answer is that you probably can use a respirator such as a CPAP or BiPap in a Lazy Daze. Many of us do so. Each of us seems to have a different way of accommodating that need. Do a bit of checking first to be sure that your unit will work. That means determining what and where your power source will be, how much power you need and how much is available, and how to make the connection from RV power to your respirator.
My new one is 24 volt, 1.75 amp, or about 120 watts.