You might be more tired after naps longer than 30 minutes because you’re waking up in the middle of a sleep cycle. The phenomenon of waking up tired post-nap is called sleep inertia, and while it’s more common in longer naps, it can happen with any nap length. To combat sleep inertia, try to get up and walk around right when you wake up from a nap. The drowsy feeling should dissipate within a couple minutes.