An interesting and somewhat related fact is that flying birds also sometimes sleep: https://www.audubon.org/news/scientists-finally-have-evidenc...
The short story (at least in the case of the frigatebirds they studied) is that they do hemispherical sleeping, where only one half of their brain is asleep. And also it seems they only sleep while climbing in a thermal updraft. The theory being that "gliding up" is the safest portion of their flight.
Relatadely there is a famous videoclip of a paraglider colliding with an eagle mid-flight. https://youtu.be/g8_hyqlQXpk?si=alAvnt4Xva4RGYw3 (The clip is quite scary, but both the pilot and the eagle seems to be fine at the end.)
It is speculated that the incident happened because the bird was "dozing off" mid-flight in the updraft too. Of course this is difficult to verify.