First: Karoshi.
Yongzheng period was the most brilliant moment of the Qing Dynasty. I do my duty to revise the memorial every day and make extra efforts to improve people's food, clothing, housing and transportation. Even in order to observe the people's feelings in various places, I didn't rest for a year, and I was so tired that my body collapsed.
Second: Yongzheng was stabbed to death by Lv Siniang.
Lv Siniang's family had the idea of fighting against the Qing Dynasty and regaining sight, but it was later known by Yongzheng, so they ordered all the men of Lv Siniang's family to be beheaded, while the women were sent away and even reduced to slaves. Unfortunately, Lv Siniang escaped for some reason and vowed to avenge his family. The only way for a woman to get revenge is to assassinate her in the palace, which is often seen in TV dramas. And when Yongzheng died, E Ertai's trousers were covered with blood, which can prove that Yongzheng was injured.
Third: long-term use of Dan medicine to death.
Yongzheng's illness worsened, and the imperial doctor in the palace was at a loss. So Yongzheng began to recruit folk doctors, and Li Wei brought a Taoist named Jia Shifang to Yongzheng. After his treatment, Yongzheng's condition began to improve, but before long, the Taoist priest was executed by Yongzheng. It is possible that there is Wushi powder in Dan medicine, which is addictive. When Yongzheng discovered that Dan medicine was harmful, his body had already been destroyed by Dan medicine.
The above is just speculation. After all, there is no record in history. I think it's more likely to die in disgrace. Otherwise, so many people were around Yongzheng who died of illness at that time, but no one dared to explain the cause of Yongzheng's death.