Sweating sickness
Sweating sickness, also known as the "English sweate" (Lat. sudor anglicus), was a mysterious and highly virulent disease which struck England and later Europe in a series of epidemics, the first beginning in 1485 and the last in 1551, afterwards apparently vanishing.  The onset of symptoms was dramatic and sudden, with death often occurring within hours.  Its cause remains unknown.
An unrelated medical condition, hyperhidrosis, is also sometimes known informally as sweating disease.

# Repeated epidemics
Sweating sickness first came to the attention of physicians at the very beginning of the reign of Henry VII. It was known, indeed, a few days after the landing of Henry at Milford Haven on 7 August 1485, as there is clear evidence of its being spoken of before the Battle of Bosworth Field on 22 August.  Soon after the arrival of Henry in London on 28 August, it broke out in the capital. There, it killed several thousand people by its conclusion in late October that year. Among those killed were two lord mayors, six aldermen, and three sheriffs. This alarming malady soon became known as the sweating-sickness. It was regarded as being quite distinct from the plague, the pestilential fever or other epidemics previously known, not only by the special symptom which gave it its name, but also by its extremely rapid and fatal course.
From 1485 nothing more was heard of it until 1507, when the second outbreak occurred, which was much less fatal than the first. In 1517 was a third and much more severe epidemic. In Oxford and Cambridge it was frequently fatal, as well as in other towns, where in some cases half the population are said to have perished. There is evidence of this outbreak spreading to Calais and Antwerp, but with these exceptions it did not yet spread beyond England.
In 1528 the disease recurred for the fourth time and with great severity. It first showed itself in London at the end of May and speedily spread over the whole of England, though not into the far north of England, Scotland or Ireland.  In London the mortality was very great; the court was broken up, and Henry VIII left London, frequently changing his residence. It is believed that Anne Boleyn may have contracted and survived the sickness.  The most remarkable fact about this epidemic is that it spread over Europe, suddenly appearing at Hamburg and spreading so rapidly that in a few weeks more than a thousand people died.  Thus was the terrible sweating-sickness started on a destructive course, during which it caused fearful mortality throughout Eastern Europe.  It spread much in the same way as cholera. It arrived at Switzerland in December, then northwards to Denmark, Sweden and Norway, and then eastwards to Lithuania, Poland and Russia.  It never appeared in France or Italy.  It also emerged in Belgium and the Netherlands, probably transmitted direct from England as it appeared simultaneously in the cities of Antwerp and Amsterdam on the morning of 27 September.  In each place which it infected, it prevailed for a short time, generally not more than a fortnight.  By the end of the year it had entirely disappeared, except in eastern Switzerland, where it lingered into the next year.  After this, did not re-appear on mainland Europe.
The sweating sickness did reach Ireland in 1492 when the Annals of Ulster (vol.iii, ed. B. MacCarthy, Dublin, 185, pp 358f.) record the death of James Fleming, baron of Slane from the plaigh allais, newly come to Ireland. The Annals of Connacht (ed. A.M.Freeman, Dublin, 1944, pp 594f.) also record this obit, and the Annals of the Four Masters (vol.iii, ed. J.O'Donovan, Dublin, 1856, pp 1194f. record 'an unusual plague in Meath ... of 24 hours' duration; and any one who survived it beyond that period recovered. It did not attack infants or little children.' Note, however, that Freeman in his footnote to AConn. denies that this 'plague' was the Sweating Sickness, in spite of the similarity of the names, but 'Relapsing or Famine Fever', possibly Typhus (but ?).

## The final outbreak
The last major outbreak of the disease occurred in England 1551.  An eminent physician, John Caius, wrote an eyewitness account of the disease at this time called A Boke or Counseill Against the Disease Commonly Called the Sweate, or Sweatyng Sicknesse.

# Symptoms
The symptoms as described by Caius and others were as follows. The disease began very suddenly with a sense of apprehension, followed by cold shivers (sometimes very violent), giddiness, headache and severe pains in the neck, shoulders and limbs, with great exhaustion. After the cold stage, which might last from half-an-hour to three hours, followed the hot and sweating stage. The characteristic sweat broke out suddenly without any obvious cause. Accompanying the sweat, or after that was poured out, was a sense of heat, headache, delirium, rapid pulse, and intense thirst. Palpitation and pain in the heart were frequent symptoms. No skin eruptions were noted by observers including Caius. In the final stages, there was either general exhaustion and collapse, or an irresistible tendency to sleep, which was thought to be fatal if the patient were permitted to give way to it.  One attack did not offer immunity, and some people suffered several bouts before succumbing.
The malady was never seen again in England after 1578 although a similar illness, known as the Picardy sweat, occurred in France between 1718 and 1861, but was less likely to be fatal and was accompanied by a rash which was not a feature of the earlier outbreaks.

# Cause
The cause is the most mysterious aspect of the disease.  Commentators then and now put much blame on the general dirt and sewage of the time which may have harboured the source of infection.  The first outbreak at the end of the Wars of the Roses means that it may have been brought over from France by the French mercenaries whom Henry VII used to gain the English throne, particularly as they seem to have been immune.  The fact that the disease seems to have been more virulent among the rich than the poor suggests why it was judged noteworthy in comparison to the other illnesses of the time.  Relapsing fever has been proposed as a possible cause.  This disease, which is spread by ticks and lice, occurs most often during the summer months, as did the original sweating sickness.  However, relapsing fever is marked by a prominent black scab at the site of the tick bite and a subsequent skin rash, whereas contemporaries did not note these relatively obvious symptoms, so the identification is far from certain.  
More recently, Hantavirus has also been proposed, and appears to be an interesting candidate for consideration in the etiology of this illness. However, certain clinical features of Hantavirus outbreaks do not seem to match the progression of the sweating sickness; specifically, while Hantavirus has only rarely been observed to be transmitted from one human to another, this is believed to be a significant mode of transmission of the sweating sickness.  Although HPS outbreaks share a very similar clinical picture with descriptions of the sweating sickness, a number of questions yet to be answered leave the door open to other theories of etiology.