But once the nap lasted beyond about the twenty-minute mark, our body and brain began to pay a price.52 That price is known as “sleep inertia”—the confused, boggy feeling I typically had upon waking. Having to recover from sleep inertia—all that time spent splashing water on my face, shaking my upper body like a soaked golden retriever, and searching desk drawers for candy to get some sugar into my system—subtracts from the nap’s benefits, as this chart makes clear.
