What is the meaning of "O Allah, I seek refuge in Your greatness from being assassinated from beneath me" in the Hadith?

It was narrated from Ibn Umar (may Allah be pleased with them both) that the Messenger of Allah (peace and blessings of Allah be upon him) never abandoned these words, morning and evening: "O Allah, I ask You for pardon and well-being in this world and the Hereafter. O Allah, I ask You for pardon and well-being in my religion, my worldly affairs, my family, and my wealth. O Allah, conceal my faults and calm my fears. O Allah, protect me from before me and from behind me, from my right and from my left, and from above me, and I seek refuge in Your Greatness from being unexpectedly destroyed from beneath me." Narrated by Abu Dawud, An-Nasa'i, Ibn Majah, and Al-Hakim.