Grave; Sleep and Death
Sleeping is considered to be the smaller death it is so similar to the real death in which soul leaves body. This asleep may see now a disturbing dream and wishes to escape from it or a nice dream and wishes not to end. But his body is here and didn't move and we can't know what he is seeing.
There are too many things that our senses can't perceive. For example the apparatus which is made to protect us from harmful animals spread sound waves which are too disturbing and agonizing to these animals however, our senses can't perceive it.
The grave that lies before us for thousands of years, the man inside is in happiness or sadness, but we can't see or hear what he feels because he is in another world not like our world. It is not the world of dreams but it is much bigger and wider one, it is the world of barzakh (isthmus), a world that separates between our world and the eternal hereafter.
What does the dead see?
We hear about the paradise and what is there from delight and enjoyment and we hear about the hell and what is there from misery and torture, but do we know the form of the paradise and the type of enjoyment there or do we know the form of the hell and the type of torture there?
When a dead is put in his grave a window to the paradise or the hell is opened to him. This window is not like the windows we know but it is unseen window from the hereafter which only dead people can see.
Here the dead see the paradise in reality not imagination. Not only that but also he receives its enjoyments and delights till the Day of Resurrection.
And as the prophet (PBUH) said the period that passes on the dead is like the period between Al-zuhr and Al-aasr prayer which is about 3 hours.
And don’t be astonished that a period of thousands of years can pass in only 3 hours, because the man doesn't feel time passing when he is happy and vice versa.