“Sunlight in the morning affects your circadian rhythm, setting your body clock for the day and signaling you that it’s time to wake up,” Dr. Jeff Rodgers, DMD, D-ABDSM, D-ASBA, a sleep expert and dental sleep medicine practitioner, tells Bustle. This is likely to happen even if you’re feeling tired, and even if you’d really like to continue sleeping in. For most of us, falling back asleep in the daylight just won’t feel right.

For many (lucky) people, sleeping entails closing their eyes, drifting off, and waking up rested, ready to take on the day. For others, though, the nighttime routine involves walking around in their sleep, or even chatting up a storm while soundly snoozing. Dr. Rodgers offers his insight into the topic.