I had Fifth's disease in highschool in Louisiana. Knocked me out of school for 6 weeks.
I had a temperature of 104 for a week and finally had to go to the hospital and get an IV because I was becoming dehydrated.
Fifth's? It was probably mono. Only people with AIDS, sickle cell disease, hereditary spirochaetosise, cancer or who are unborn have a tough time with Fifth's.