1)
Who was with him?
1.
Rashi citing Megilah 3a: Chananyah, Misha'el and Azaryah.
2)
Why did a great fear seize them?
1.
Rashi citing Megilah 3a: If one is frightened and does not know why, it is because his Mazel in Shamayim saw something.
2.
Malbim: Because they were Nevi'im, they sensed the matter, even though they did not see the vision. He was at a higher level than them (Megilah 3a).
