Or maybe you stare wistfully out your window pondering the meaning of it all. Whether you call it seasonal affective disorder (SAD), seasonal depression, or winter blues, it's very common for your mood to take a dip when autumn arrives. Though scientists are still teasing out all the causes, changes in multiple hormores and neurotransmitters, like cortisol, are at least partly to blame. Cortisol levels are closely linked with sleep-wake cycles and light exposure. Overnight, your levels typically increase gradually and then burst in the morning as the sun rises, in what's known as the cortisol awakening response. With darker days, some folks don't get that burst and remain sleepy and fatigued and moody during the day.
"Scientists also have demonstrated seasonal changes in dopamine and serotonin—two neurotransmitters that are intimately tied to depression," says neurologist and sleep specialist W. Christopher Winter, MD, author of The Sleep Solution. Regular exercise—especially outdoors in the daylight—can help brighten your mood and stave off SAD.
Related: 6 Foods To Boost Your Mood This Winter