Nature of Life in the Grave
Question

When it is said that the dead person is alive in the grave, is that the same as his former life (is he alive in the same way)? How many of his senses are restored to him? For how long does he stay alive in the grave?
If the dead person is questioned in a physical sense, how does that apply in the case of those who are burned (cremated) like the Hindus and Japanese and others?
Where does their questioning take place?  When a doctor performs an operation, he removes the person's senses by means of an anaesthetic. With regard to death, I wonder what death means.
Praise be to Allah.Muslims’ belief about the Unseen
Firstly: it should be noted that what is obligatory upon every believing man and woman is to believe what Allah tells them in His Book or on the lips of His Messenger (peace and blessings of Allah be upon him) about all matters that have to do with the Hereafter, the Reckoning, Paradise and Hell, or that have to do with death, the grave and torment or blessing in the grave, and all matters of the Unseen that are mentioned in the Noble Quran or in the authentic reports of the Sunnah. We have to believe and accept that, because we know that our Lord tells the truth in all that He says and tells us about. Allah says (interpretation of the meaning): 
“and whose words can be truer than those of Allah? (Of course, none).” [al-Nisa4:122]
“And who is truer in statement than Allah?”[al-Nisa 4:87] 
We know that the Messenger of Allah (peace and blessings of Allah be upon him) is the most truthful of people, and that he never spoke on the basis of his own whims and desires; it was Revelation which was revealed to him. Whatever was proven in the authentic hadiths, it is obligatory to believe in it even if we do not fully understand it. 
So what we have to do is to believe what has been narrated concerning the matters of the Hereafter and of Paradise and Hell , and the blessings of the people of Paradise and the torments of the people of Hell, and the fact that in the grave a person will be tormented or blessed, and that his soul will return to him. All of this is true and is stated in the texts, so we have to submit to that and believe everything that we learn from the Quran or that is narrated in the authentic Sunnah or on which the scholars of Islam reached consensus. 
If Allah blesses a believing man or woman with knowledge of the reasons for that, then it is even better, light upon light and knowledge upon knowledge. So let him praise Allah and give thanks to Him for the knowledge and insight that He has bestowed, thus increasing his knowledge and peace of mind. 
Questioning in the grave
With regard to the questioning in the grave and the state of the deceased, this questioning is real. The deceased person’s soul will be restored to him; authentic reports to that effect have been narrated from the Messenger (peace and blessings of Allah be upon him). 
Life in the grave
The life of the deceased in the grave is different from his life in this world; it is a special kind of life in al-barzakh (the interval between his death and the Day of Resurrection) which is not like his life in this world, where he needs food and drink etc. It is a special kind of life wherein he can understand the questions and answers, so the two angels will ask him, Who is your Lord? What is your religion? Who is your Prophet? 
The believer will say, My Lord is Allah, Islam is my religion and Muhammad is my Prophet. This will be the answer of believing men and women. Then he will be asked, What do you know about this man (Muhammad (peace and blessings of Allah be upon him))? He will say, He is the Messenger of Allah. He brought us guidance and we believed in him and followed him. It will be said: we knew that you were a believer. Then a gate to Paradise will be opened for him, and he will feel its rest and provision and blessings. It will be said, This is your place until Allah resurrects you to it. And he will be shown his place in Hell, and it will be said to him, This would have been your place if you had disbelieved in Allah, but now Allah has granted you refuge from it and you have ended up in Paradise. 
As for the non-Muslim, he will be asked about his Lord and his religion and his Prophet, and he will say, Oh, oh, I don’t know, I heard the people saying something so I said the same. Then he will be beaten with an iron rod and will utter a scream that will be heard by all things apart from al-thaqalayn, i.e. jinn and men; the animals will hear it. Then a gate to Hell will be opened for him, and his grave will constrict until his ribs intermingle, and his grave will be like one of the pits of Hell. A gate to Hell will be opened for him and he will feel its heat and torment . It will be said, This is your place until Allah resurrects you to it. Then a door to Paradise will be opened for him and he will be shown his place in Paradise, and it will be said to him, This would have been your place if Allah had guided you. 
From this, we know that the grave will be either one of the gardens of Paradise or one of the pits of Hell. The torment or blessing will happen to the body as well as the soul in the grave, and also in the Hereafter, in either Paradise or Hell.
Will those who die by drowning or burning be punished in the grave?
With regard to those who die by drowning or burning, or are eaten by wild animals, their souls will have their share of torment or blessing, and that will come to their bodies on land or in the sea, or in the bellies of the wild animals, as much as Allah wills. But most of the blessing or torment will come to their souls which remain, either in a state of blessing or a state of torment. 
The soul of the believer will go to Paradise; the Prophet (peace and blessings of Allah be upon him) said: “The soul of the believer is a bird which hangs from the trees of Paradise, eating their fruits; the soul of the disbeliever goes to Hell.”
Every Muslim man and woman has to accept what Allah and His Messenger (peace and blessings of Allah be upon him) have told us, and believe it as it was meant by Allah, even though some of the meaning may be hidden from us. And Allah has perfect wisdom, may He be glorified.
And Allah knows best.