Explanation of the meaning of the verse "Indeed, We will cast upon you a heavy word"

It is narrated from Sayyidah Aishah (may Allah be pleased with her) that when revelation came down upon the Prophet (peace and blessings be upon him) while he (peace and blessings be upon him) was riding his she-camel, she would rest her neck on the ground (from the weight of the revelation) and would not have the strength to move. Then she recited the saying of Allah, the Mighty and Majestic: "Indeed, We will cast upon you a weighty word" [Al-Muzzammil: 5].
This hadith has a sahih (authentic) chain of narration, but the two Shaykhs (Bukhari and Muslim) did not record it.

It is narrated from Sayyiduna Abdullah bin Mas'ud (may Allah be pleased with him) concerning the saying of Allah Almighty: "Indeed, the rising by night" [Al-Muzzammil: 6], that he said: In the Abyssinian language it means qiyam al-layl (standing at night for worship).
This hadith has a sahih (authentic) chain of narration, but the two Shaykhs (Bukhari and Muslim) did not record it.

It is narrated from Sayyiduna Abdullah bin Abbas (may Allah be pleased with them both) concerning the saying of Allah Almighty: "And food that chokes" [Al-Muzzammil: 13], that he said: It refers to a thorn that gets stuck in the throat, neither going in nor coming out. And concerning the saying of Allah Almighty: "a heap of sand pouring down (mahil)" [Al-Muzzammil: 14], he said: "Mahil" is that (heap of sand) from which, when you take something, the rest of it (slides and) follows you; and by "kathib" is meant a heap of sand.
This hadith has a sahih (authentic) chain of narration, but the two Shaykhs (Bukhari and Muslim) did not record it.