It's as simple as 411 says. Agree between you if you want or need a nap.
To the CC, I just tell them that there will be one or other of us taking a power nap, don't ding on the call button, but just talk on the interphone (which is being monitored), and I'll answer, if they really feel in the need to do the 20 minute check. Mostly, I'll call them just to let them know that all is well.
It's another situation that SOPs gallore can be written for, but is best sorted with common sense. If comon sense doesn't start off by recognising that it is good practice, then all the SOPs in the world are not actually going to make life any better, just more tiring.