Naps are awesome, but they’re not all equally restorative. Depending on how long you nap, you might end up feeling groggy when you wake up. Aim for about 20 minutes if you want a boost in energy and mental alertness. Anything longer than that and you risk feeling worse than before, or elongating that groggy feeling for even longer. Also, though it might seem counterintuitive, try drinking coffee just before your power nap. The caffeine will kick in by the time you wake up, helping give you the boost you were hoping for.