National Sleepy Head Day is based on the belief that whoever sleeps the latest on that day will be tired all year and is the “sleepyhead of the year”. The “sleepyhead” is woken up with water; for example, by throwing them into a lake or sea. The day is based on an old Christian myth of the Seven Sleepers of Ephesus who hid in a cave to escape persecution around 250 AD.
Another common belief is if it rains on the day, it will rain for the next 7 weeks.
Image: National Sleepy Head Day (Finnish: Unikeonpäivä) in the city of Naantali, Finland by Markus Rantala. CC-BY-SA-3.0 via Wikimedia Commons.