Question: death and state after death.
Before we get into the realm of fantasy, let me declare: this is a taboo subject! It means that man is unaware of this because it is part of the Invisible World, which is an area blocked from man. So, human thoughts and ideas about death and its subsequent state are considered to be sin in Islam.
The only thing we can know about this state that Allah (SWT) tells us in the Quran. No more, no less. Therefore, I bring up more Quranic quotes than usual, because without them I would find myself in the world of superstitions. A lot of Hadith could be cited here too, but then the scope would reach beyond the comfortable readability.
The whole concept is based on the duality of body and soul. The body is material, transient, and the soul is deposited with us by Allah, is non-material and eternal from the time of its placement. Islam does not believe in reincarnation. We believe in one trial period what we call according to our human terminology earthly life. For a believer, it is not a correct definition because the earthly life doesn't exist alone. There is a life even beyond that where the body is no longer involved.
Every soul shall have a taste of death: And only on the Day of Judgment shall you be paid your full recompense. Only he who is saved far from the Fire and admitted to the Garden will have attained the object (of Life): For the life of this world is but goods and chattels of deception. (Quran 3:185)
The soul will not die; but the death of the body will give a taste of death to the soul when the soul separates from the body. The soul will then know that this life was but a probation. And seeming inequalities will be adjusted finally on the Day of Judgment.
One can feel the coming of the death. Allah (SWT) sends angels in our lifetime to support us and at the time of death, too. The latter angel (malak al-maut) comes to tear our soul out or lift it gently from our bodies. In our brain, the medieval imagery creates a winged being as an angel. In fact, we don't know what an angel looks like. It's a creature that implements Allah's instructions.
He is the irresistible, (watching) from above over His worshippers, and He sets guardians over you. At length, when death approaches one of you, Our angels take his soul, and they never fail in their duty. (Quran 6:61)
But how (will it be) when the angels take their souls at death, and smite their faces and their backs? (Quran 47:27)
It is all very well for them to practice hypocrisy in this life. How will they feel at death, when they find that the angels know all, and touch the very spots they had taken such care to conceal?
Similar reference in 6:93)
(In Falsehood will they be) Until, when death comes to one of them, he says: "O my Lord! send me back (to life),- (Quran 23:99)
At this point, it should be noted that once the death is near there is no longer way to repent our sins. Up until now, we may repent, or be able to compensate our earthly sins, but it's too late in the hour of death.
After the separation of soul and body, the body returns to the cycle of the material transience. It will once resurrect with the permission of Allah (SWT), but in what dimension, where and when, it also belongs to the domain of philosophy. We don’t know. We only know as much as the Quran says. Nor does the soul go immediately to Heaven or Hell. It enters into a transition state called Barzakh.
This word is mentioned twice in the Quran. 55:19-20 denotes the wall separating the two oceans. It can be a partition between salt and fresh water, but figuratively it can also mean the partition between human knowledge and the Invisible World.
Other times, we meet Barzakh after death. Using the terminology of IT this is the interface. An intermediate state in which there is no time-space dimension, only to maintain the existence of the soul until the Final Judgment comes. Some use to call the separation of the body-soul a small death, the one after the Final Judgement a great death.
"In order that I may work righteousness in the things I neglected." - "By no means! It is but a word he says."- Before them is a Partition till the Day they are raised up. (Quran 23:100)
The unrighteous will ask for another chance. But it will be too late then. The time for repentance will then have passed.
We have come to the Final Judgement. Then our earthly body resurrects. Our organs, hands, feet, tongues, will testify against us or for our benefit in the course of reckoning.
Then when the Trumpet is blown, there will be no more relationships between them that Day, nor will one ask after another! (Quran 23:101)
The old relationships of the world will then be dissolved. Each soul will stand on its merits.
Then those whose balance (of good deeds) is heavy,- they will attain salvation: (Quran 23:102)
But those whose balance is light, will be those who have lost their souls, in Hell will they abide. (Quran 23:103)
The loss or perdition will not mean that they will die and feel no more: 14:17. The punishment will mean nothing, if there was no sensibility, but total annihilation.
After the Final Judgment, our souls are settled in the place they deserve. The body will be permanently destroyed, the soul retaining the ability to perceive remains.
If there is a question, whether there is a returning or visiting soul, etc., this is also an area for which there is no earthly knowledge or authority to reveal it.
May Allah, accept my answer and forgive me if I am wrong.