Also, that is the net energy expenditure of the body, but not the input required. We use a relatively antiquated form of the internal combustion engine to turn food into energy, which seems to be around 25% efficient, at best. It's also built on chains of other fairly inefficient biological entities, so it's hard to say what the overall efficiency is, but suffice to say that we're prevented from using the most efficient energy sources.

> during which it doesn't do much

I know this was in jest, but if sleep was not a critical biological process we would have evolved to not do it already

It's basically a cleaning cycle for the brain. If we don't sleep we die pretty soon. Meaning it's necessary daily scheduled maintenance downtime, which should count directly to efficiency calculations!