A recent study was published suggesting he died of Guillain-Barré Syndrome, an auto-immune disease, which would have paralyzed him and would have explained his inability to move or speak. Interestingly, his body did not begin decomposing until 6 days after his death.

https://ancienthistorybulletin.org/downloads/katherine-hall-...

https://www.sciencedaily.com/releases/2019/01/190122115006.h...