Scientists have discovered why some people are perky morning people and others are morning grouches! And it all boils down to something called “sleep inertia.”

Dr. Allison Harvey is a psychology professor and she says that when we wake up, “sleep inertia” is the period of grogginess, irritability and moodiness that usually lasts between 5 and 20 minutes. And then most of us snap out of it, and go about our day.

But some people are stuck in “sleep inertia” – AKA grouchy mode - for hours – and spend their mornings complaining about everything from traffic to their botched soy latte! But all that negativity is a huge turn-off to others – and it’s no good for you, either. It could mean getting passed over for a promotion, or having fewer friends.

So, why are some of us stuck in grouchy mode? Two reasons: either you’re not getting quality sleep, or there’s something wrong in your life on an emotional level. If you only get grouchy on workday mornings – but wake up happy as a clam on your day off – that may be your answer right there. You may not like your job. If you get grouchy on days when your to-do list is a mile long, you may feel overwhelmed.

There’s no cure for sleep inertia, but the less time in you’re in that phase, the better. So, as soon as you wake up, open the curtains and turn on the lights! The more light you’re exposed to, the faster your brain will get out of sleep-mode. Then, pump up your feel-good endorphins by going on a morning walk or calling a friend on the commute to work. And drinking coffee is an effective way to counteract sleep inertia. Because the faster you snap out of it, the better your mood and day will be.