Conditions before the demise
The Holy Prophet (Sallallahu alaihi wa sallam) would enjoy uninterrupted manifestations from Allah Most High. However, as the time of His passing away came closer, He (Sallallahu alaihi wa sallam) would be all the more engrossed in the proximity of Allah and divine visions because of which strange effects were seen on the blessed body of the Holy Prophet (Sallallahu alaihi wa sallam). Externally, sometimes there would a lot of pain in His head and sometimes, there would be a spike in fever and sometimes, He (Sallallahu alaihi wa sallam) would faint. All these were physical manifestations if the absorption of the Holy Prophet (Sallallahu alaihi wa sallam) in the divine manifestations.
At the end of Safar, the Holy Prophet (Sallallahu alaihi wa sallam) visited Jannatul Baq’ee. While returning, He started having a headache, as mentioned in this Hadith of Musnad Imam Ahmed bin Hambal:
Translation: It is narrated on the authority of Hadhrat Abu Muwaihib (May Allah be well pleased with him), slave of the Holy Prophet (Sallallahu alaihi wa sallam), he says: The Holy Prophet (Sallallahu alaihi wa sallam) sent for me in the middle of the night and said: O Abu Muwahib! I have been ordered to seek forgiveness for those who are in Baq’ee. You also come with me. I went along with the Holy Prophet (Sallallahu alaihi wa sallam). When He stood in Baq’ee, He said: Assalaamalaikum Ya Ahlal Maqabir! Peace be upon you o people of the graves. The way you start your day is better than the way in which people start it if you would realize what Allah Most High has saved you from. Trials are near like the phases of the dark night whose last part comes after the first. The last trial is worse than the first one. Hadhrat Abu Muwaihib (May Allah be well pleased with him) says: Then the Holy Prophet (Sallallahu alaihi wa sallam) turned to me and said: O Abu Muwaihib! I had been granted the keys to the treasures of the world and stay in this world, then was granted paradise, and I was given the authority to choose between meeting my Lord and paradise. I said: May my mother and father be sacrificed for you! Take the treasures and stay of this world. After that paradise. The Holy Prophet (Sallallahu alaihi wa sallam) said: O Abu Muwaihib! By Allah! Verily, I have chosen meeting my Lord and paradise. Then the Holy Prophet (Sallallahu alaihi wa sallam) prayed for the forgiveness of those buried in Baq’ee and returned. The next morning, the sickness started in which Allah Most High drew His blessed soul. (Musnad Imam Ahmed bin Hambal, Hadith No. 16419)
Because of absorption in divine manifestations, there was apparent pain and because of the intensity of pain, there was a fever spike. The fever was so high that it was felt at touch. In spite of all this, the Holy Prophet (Sallallahu alaihi wa sallam) would go to the Masjid Nabawi and lead the Salaat. He would also observe the order of the Mothers of the Believers in spite of the fact that the way it is Compulsory (Wajib) for Muslims to assign turns if there are multiple wives and observe it, it is not Compulsory on the Holy Prophet (Sallallahu alaihi wa sallam) to do so. However, the Holy Prophet (Sallallahu alaihi wa sallam) had done so out of benevolence. When this condition intensified, He (Sallallahu alaihi wa sallam) summoned all the Wives and expressed His desire to stay with Hadhrat ‘Aisha (May Allah be well pleased with her). At this time, the Holy Prophet (Sallallahu alaihi wa sallam) was with Hadhrat Maimoona (May Allah be well pleased with her). All the Wives expressed their assent. Only then did the Holy Prophet (Sallallahu alaihi wa sallam) came to the room of Hadhrat ‘Aisha (May Allah be well pleased with her).