Three answers...there is a "day nap" place opening in the next few weeks in the D terminal. No idea on cost but it will be thee soon.

There are also two Hyatt hotels literally in airport. Yes, you'd have to go back through security, but a small price to pay for 4 hours of sleep.

Lastly, the AAdmirals club in the D terminal regularly has people napping in sleeper-type recliners in the back near the bar. There are also showers in D (and A).