Dying in the Desert

I read that after the Exodus the Jewish People died in the desert after 40 years — and that they just lay down in a ditch and died. Did Moses tell them when to lie down and die? If not – how did they know when to build a ditch and lie down in it? Did they all die at the same time?

The Sages teach that after the Sin of the Spies God decreed that all men between the ages of twenty and sixty were to die in the wilderness. They died once a year on the anniversary of the spies' return and all the men would dig their own graves get in them and go to sleep that night. In the morning many of them would not wake up as they had died in their sleep. This continued until the final year in the wilderness when everyone woke up the next morning which heralded the end of the decree.