What are the symptoms of sleep inertia and how does it make it hard to wake up?
A large body of research shows that naps improve cognitive performance and boost mental and physical health. In many ways, naps are Zambonis for our brains. They smooth out the nicks, scuffs, and scratches a typical day leaves on our mental ice. Naps needn't be long to be effective. In fact, extremely short naps can give you a boost without creating what biologists call "sleep inertia."
Finding it hard to get up is often a biological problem, where the systems in our brain that control our sleep have got out of sync. This creates sleep inertia, the inability to feel alert and perform when we first awake.
How Naps Affect Your Brain and Why You Should Have One Every Day: Sleeping for the wrong length of time can give you sleep inertia—that feeling of waking up groggy and even more tired than you were before.