I am addressing the OP's question directly.
He and some respondents are off-the-rails with his energy assumptions. You are fortunate with not having problems with your unit. All assisted breathing apparatus comes with an instruction booklet. Inside that booklet you will find specific reference to unplug the unit from 12vdc before the vehicle engine is started. Capiche?
Actually looking with your own personal eyeballs at CPAP and BiPAP circuit boards will show an absolute minimum of transient voltage protection. If you want to risk your personal equipment, that is your concern. I am reporting what I see.