"It is believed that the Egyptians greatly feared these days due to the prevalence of plague and disease, attributed to the wanderers (SmAjw) and slaughterers (xAtjw) of the goddess, Sekhmet, which were particularly rife at the end of the calendar year. Magical texts, such as the Book of the Last Day of the Year on Papyrus Leiden I 346, were recited in order to pacify the goddess, and rituals were performed, for example, the application of linen bandages inscribed with certain deities to the throat to ward off the effects of plague." (source: egyptianaemporium.wordpress.com)
"The Egyptian year was divided into twelve months of thirty days each, which means that each year was about five days short of the astronomical year. To compensate for this difference, five extra days were added to the year, called epagomenal days. Because they were not part of the normal year created by the gods, the Egyptian regarded these days as particularly ominous, and texts have survived listing exactly what may and may not be done during this period." (source: globalegyptianmuseum.org)
Known as the "birthdays of the gods" in the Egyptian calendar, the epagomenal days were celebrating the birth of: 1 Osiris 2. Horus 3. Set 4. Isis 5. Nephthys.