Naps are great, but not all are equally restorative. According to how long do you take a nap, you might end up feeling dizzy when you wake up. Aim for around 20 minutes if you want a boost of energy and mental alertness. Anything longer than that and you might feel worse than before, or make that groggy feeling even longer. Also, while it may seem counterintuitive, try drinking coffee right before your nap. The caffeine will kick in the moment you wake up, helping to give you get the boost you were hoping for.