Please don't flame me on this, because I don't have my books available to make direct quotes.
With regards to disease first, In Egypt during the Mamluk period, 1250-1517 AD, the biggest single killer of
mamluks was not battle but
'Ta'oon', the Plague. Goodness knows when the
mamluks weren't fighting Crusaders or Mongols, they were busy fighting each other in the countless power struggles of the Emirs. So that was a lot of
Ta'oon.
The
mamluks also tended to wear relatively heavy armour: mail, lamellar armour, mail-&-plate armour or brigandines and helmets with mail coifs. These were men originally from the Steppes of Central Asia, the Crimea and the Caucasus, having to fight in the Heat of Egypt, Palestine and Syria in heavy armour, yet I don't recall any referrences to men dying of heat stroke. However numerous Egyptian chroniclers like Ibn Iyas, El-Maqrizi and El-Ayni also pointed out that armour was not put on until the men were just about to go into battle. But in at least one battle fought against the Mongols in the early 14th century (it may have been Marg Es-Safar, correct me if I'm wrong) the
mamluks remained in the saddle all night, fully armoured, and did not start fighting the Mongols till the morning. The same Egyptian historians are quick to point out when the Mongols and Cruasaders were collapsing from thirst and exhaustion.