47. For the explanation of the blowing of the Trumpet, see (E.N. 78 of Surah TaHa). As for the length of the interval between the first blowing of the Trumpet and its second blowing, we have no information. The interval may be of hundreds and thousands of years. Abu Hurairah has related that the Prophet (peace be upon him) said: Israfil has put the Trumpet to his mouth and is looking up to the divine Throne, awaiting orders for blowing it. The Trumpet will be blown thrice.
On the first blowing, called nafakhat al-faza, everything in the earth and heavens will be struck with terror. On the second blowing, called nafakhat as-Saaq, everyone will fall down dead. Then, when none shall remain except Allah, the One, the Everlasting, the earth will be changed altogether and will be spread flat and smooth without a crease or wrinkle on it. Then Allah will administer a rebuke to His Creation, whereupon everyone will rise at the spot where he had fallen dead, on the changed earth, and this will happen on the third blowing of the Trumpet called nafakhat al qiyam li-Rabbil-Alamin. This is supported by several allusions in the Quran also.
For example, see (Surah Ibrahim, Ayat 48); (Surah TaHa, Ayats 105-108), and the E.Ns thereof.
48. That is, at that time they will not realize that they had been dead and had been raised back to life after a long period, but they will be thinking that they had fallen asleep, and had been woken up suddenly by some terrible catastrophe, and were running away from it. (For further details, see Surahs (TaHa, Ayat 103); (Al-Hajj, Ayats 1-2).
49. Here, it is not clear as to who will give this answer. It may be that they themselves would realize after some time to their horror that it was the same thing of which the Messengers of God used to inform them and they used to belie them. It may also be that the believers will remove their misunderstanding and tell them that it was not waking up from sleep but the second life after death. And it may also be that they will understand this from the general conditions prevailing on the Day of Resurrection and the angels might tell them this.