Is being distressed by a doctor's news of death due to cancer considered disbelief (kufr), and is taking precautionary measures a religious obligation?

Summary of the Fatwa (definition): "Turning to means [causes] is a blemish in Tawhid (definition) (monotheism)" means that relying on means alone, without realizing that they operate by the will of Allah, blemishes Tawhid, because nothing affects by itself except by Allah's permission. "Completely turning away from means is a blemish in the Sharia (definition) (Islamic law)" means that abandoning means entirely, believing it to be perfect reliance on Allah, contradicts the Sharia, which commanded the adoption of means. A believer combines Tawhid with the adoption of means.

Adopting means is generally obligatory, and it is not permissible to turn away from them. As for a specific means, the ruling on adopting it varies according to its strength and benefit. Some means are obligatory, such as eating to preserve life, while some are recommended or permissible. Sometimes, abandoning a means might be better if patience is more beneficial for the Muslim. Treatment may become obligatory if its absence leads to the destruction of life or the damage of an organ.