Sleep occurs in multiple stages, alternating between deeper and lighter sleep. We sleep more and more lightly as the night goes on.

If we wake up at just the right moment in our lighter sleep stages, we’ll feel reasonably good and snap into alertness quickly.

But if we’re forced to wake up while in a deep sleep phase, we’ll feel groggy, disoriented, and sleepy — suffering from sleep inertia.

There are many gadgets and apps that will sense your sleep cycles and wake you up when you’re sleeping your lightest.

You can also track your sleep with gadgets and apps like the Fitbit, which will help you gauge where to improve your sleep and wake routines.