I really don't think it's just a legend. The linked article and Wikipedia (https://en.wikipedia.org/wiki/Segmented_sleep https://en.wikipedia.org/wiki/Segmented

I really don't think it's just a legend. The linked article and Wikipedia (https://en.wikipedia.org/wiki/Segmented_sleep https://en.wikipedia.org/wiki/Segmented_sleep) give enough evidence that it seems unlikely to be a complete myth. And saying "I hate waking up in the middle of the night" doesn't really have much to do with this. If you consistently slept for 12 hours a night, you might find it a lot easier and more pleasant to get up in the middle, and that's exactly what one of the studies in the Wikipedia article showed. And as anecdotal evidence, even a few people in this 2-hours-old comment section say they've tried it with good results.