I once tried an extreme version of this. I became single and I already didn't have a fixed work schedule, so other than societal convention there was no reason for me to adhere to any regular day-night cycle.

So I tried sleeping when I was really tired, waking up without an alarm, eating when I was hungry, etc. I ignored watches, daylight and society. For context, my internal days have always been much longer than 24 hours, often finding myself going to sleep at sunrise; so I thought this was gonna be great, not having to spend an hour awake in bed.

It was horrible. And I mean HORRIBLE. I became a zombie, even though I was sleeping more than ever. I felt deeply depressed within two days. I lost all concept of the passage of time, and could never tell how long ago something had happened. I couldn't think properly or comunicate with other people. It affected me physically too, my weight, my stomach.

The experiment didn't last long. But I couldn't tell you how long.