Sweating Sickness was a serious illness which appeared at different intervals during Tudor times and which claimed many lives. This illness, known also as the "English Sweate" affected England first, and then spread into Europe, with a series of epidemics between 1485 and 1551. It is not known exactly what caused it or even what it was because it disappeared entirely after 1578.
Symptoms of sweating sickness included "a sense of apprehension", shivers, dizziness, headaches, pain in the arms, legs, shoulders and neck, and fatigue or exhaustion. The illness had different stages - the cold shivery stage followed by the hot sweating stage. It could kill in hours.
Possible causes - There are various theories as to what caused the sweating sickness including poor hygiene, "relaspsing fever" ( a disease spread by lice and ticks) and hantavirus. None of these theories really relate 100% to sweating sickness though.
Interestingly, sweating sickness seemed to be more virulent among the higher classes. Some believe that it may have been sweating sickness which claimed the life of Prince Arthur, Henry VIII's older brother, and others thought to have suffered from it include Anne Boleyn, William Carey (husband of Mary Boleyn), who died from it, and many members of Henry's court.