Sweetening their existence in the afterlife would be the knowledge that their enemies were receiving their just desserts, infinitely harsher than those their enemies' lawyers had finagled them out of in life. Impure Egyptians would be torn to pieces by the monster Am-mit, the eater of the dead. Wayward Judeans were condemned to eternal fire in Gehenna, a vast sleep-away torture camp. By contrast, a Hindu with a karma heavy with sin faced earthly reincarnation and suffer, over and again, and again and again, this messy business of mortality. The enemies of Islam, their skins painfully regenerating after being repeatedly charbroiled away, would endure perpetual consumption by the fires of Jihannum.
Nonexistence is the absence of experience and the absence of the capability to experience.
To readers of detective fiction, it is The Big Sleep, but a sleep without dreams or wake-up calls. In such a state one cannot fret over the fact that one is dead, or that one's body is slowly turning to dust, or that one's spouse may be sleeping with one's neighbor. In fact, in such a state, one cannot even be said to be one, period. So it seems that no one truly believes that they themselves will be in a state of suffering once they are dead. Thus this fear of death we all share cannot be the fear of being dead.