Bismillahir Rahmanir Raheem
Assalamu alaikum wa rahmatuallah,
It was once said to Imam Ghazali, "We hear about the punishment that occurs in the graves, but we open graves sometimes and find nothing that indicates punishment in them. We neither see fire nor snakes nor scorpions." The Imam paused for a moment, and then said, "Consider one who is sleeping and who is having a succession of nightmares. He sees a murderer following him, snakes chasing him, or fire that is burning him. How is that? Indeed sleep is a small example when compared to the greater sleep that occurs in the grave. And pain occurs in the grave to the one who deserves it even if we do not see it with these eyes of ours."
Source: Gems and Jewels p.147