Sleeping Flu: A disease that causes the death of ponies who enter the REM stage of sleep. The symptoms include: more frequent nosebleeds, tiredness, urge to be with other ponies, weaker magic, and eventually, death and revival. Transmission is suspected to be caused by either air or direct contact. After death, they are inactive for several minutes before reviving. After revival, they begin to repeatedly say a phrase. Ponies in the advanced stages are still able to think, but are unable to control their body. There is currently no cure to the disease. Some ponies seem to be more resistant than others, but a reason has yet to be found.