Is it? Where do you get that from?
I remember the NASA doing extensive sleep studies, determining that the optimal pattern would consist of basically "naps only"?
I've been sleeping my adult life in usually 2x3-4h "shifts", which I also remember reading is a historically often used pattern. I do not see any negative effects.
I do not track my sleeping hours. I guess it started in school, where I always stayed up way too late, so I used an afternoon sleep to catch up. I continued like that.
I despise alarm clocks, I think it goes against natural sleep rhythm and is bad for mental and physical health. We should ban them in civilized societies. I see it as one of the biggest luxuries of my life that I only have to use them on very limited occasions.
I also never grasped the concept of "every Monday at 10 am, you have to be willing and able to work". I don't understand how that can be done without messing you up after a few years.
I made it a necessity to only work jobs where I can decide on my hours with sufficient flexibility. Some weeks I work 80 hours if I feel it, some weeks I work only 10 if I don't. I co-founded a couple of projects, rarely had a boss to report to, and if I did, they cared about results and not when.
People are always more than happy with my 'productivity' and amazed at my flexibility. For clients/business partners, I actually seem to be available more often in terms of time slots than others with fixed "day" hours. I also mostly work(ed) in international teams, so people are all over the place in terms of timezone anyway (and a few at a time traveling around to conferences etc).
In my relationships, we either cuddle and I stay around until my partner sleeps and I quietly get up again to enjoy the quiet late hours (some of the best productivity, if I feel it!) and then come back later, or I sleep for a few hours next to them, and wake up early. I can then use early quiet hours for myself or for work, and then without stress prepare our breakfast. My second sleep shift is flexible, sometimes as early as 8 or 9 am, sometimes as late as 4pm - but usually within a certain more limited range for some months at a time. As long as I feel it.
I actually consider this to be "normal/natural", and what most other people seem to be doing "wild". :)
For example, I do not need stimulants like coffee or sugar drinks to get through my days.