It (suffering of death) comes to them suddenly, at a time when they least expect it! (Death is the biggest suffering, as through the experience of death, one observes his essential reality and realizes how much he failed to give its due right, and that he no longer has the opportunity to compensate, falling into the suffering of deep regret.)
Sayyed Abbas Sadr-Ameli
And it shall come upon them all of a sudden, while they are not aware
Al-muntakhab fi tafsir al-Qur'an al-Karim
A punishment that surprises them and catches them unawares and reduces them to ruin