I am a very light sleeper, but if I have a warm, quiet place to sleep, I could do so at the drop of a hat. So I guess, for me, those are my requirements for a good night's sleep: warmth, quiet and a hat.
Like many people, my list of requirements must be met or I simply can't sleep. We're not so different from some animals in that regard. Have you ever seen a dog follow his behind around in circles several times before he finally plops down and closes his eyes? I'm not sure what requirement he's trying to meet here. Perhaps his nose must be facing a northwesterly direction. Maybe his tail must be out of the wind. Or maybe he's simply checking to be sure there are no fire ant hills where he intends to lie down. If I were a dog, that would be an important requirement for sleep. Birds and hamsters built their nests just so before they can sleep in them. Some people do that as well. I have a son who builds a nest before he sleeps. His requirements for sleep are many. He must have a selection of stuffed animals settled around him, at least three pillows that have never been used by anyone else, a book and a reading light in case he wakes up at night, and a glass of water on the nightstand. He also requires 3 or 4 blankets on the bed, but he only uses one because 3 or 4 make him too warm. He has convinced himself that he needs these things or he can't sleep. Some people require complete darkness. Others can't sleep without a nightlight. Some have to sleep with the door closed. Some have to sleep with the door open. This may have to do with the darkness issue, but sometimes it is a symptom of claustrophobia. My daughter needs a spinning ceiling fan to sleep, but apparently her mattress hanging half off the bed frame is not an impediment to a good night's sleep.
One son of mine needed a silky pillowcase to sleep when he was growing up, but now he needs flannel sheets to get to sleep. My oldest needs a fan, darkness and white noise. He doesn't like quiet or still air. He would be a good camper, I think. Sleeping under the stars with no moon would provide him with darkness, wind in his face and crickets chirping all night long. Although, we might see him chasing his behind around in circles before he climbed into his sleeping bag. I'm fairly certain he wouldn't want to sleep on a fire ant hill either.
My husband seems to have many requirements for sleep. Needing his own pillow is one of them. He obviously has not determined the rest of them yet because the man never sleeps. I believe one of his requirements might be that he must have the TV beaming into his eyeballs in an otherwise dark room for at least 2 hours before he will allow his eyes to close. Another requirement might be that he must first get into our bed and as soon as the bed warms up, he must whip off the blankets and expose my backside to an icy blast of air and then sleepwalk to the living room for his eyeball exercises. Another requirement is probably the fact that he must sample every salty and sweet snack in the house before he can allow himself to sleep. He is very diligent about this step. But still he can't sleep.
Since I am a light sleeper, merely requiring warmth and quiet - and his nighttime wanderings provide neither one of these - a good night's sleep is simply a lofty goal in our house.