But you are underway.
No need to yell. I hear you just fine. There is "underway" in legalese and there is "underway" in a practical sense. With a sea anchor and with close hauling you may be "underway" legally, but pretty much not "underway" in a practical sense - so as to run into something.
I know, in court there is only one interpretation. But most of us will never see the inside of the courtroom and even if we were to and you slept during the day like your judge recommends confusion would still prevail.
Going back to the original question; "Is sleeping OK?" "Yes, if you follow all the COLREGS." is the simplest, most correct answer. But how does that provide a functional answer for the guy wanting to do his first single handed multiday excursion?
That is all I was trying to do. Configure yourself so you are not moving, make yourself visible and do what you need to do. Not sleeping will make you more dangerous than you would be if not moving and clearly visible.
(where's the peace sign smilie?)