Albert Barnes Commentary Daniel 8:1

"In the third year of the reign of king Belshazzar a vision appeared unto me, even unto me, Daniel, after that which appeared unto me at the first." — Daniel 8:1 (ASV)

In the third year of the reign of king Belshazzar - Regarding Belshazzar, see Introduction to Daniel 5:0, Section II.

A vision appeared to me - This vision appears to have occurred to him when awake, or in an ecstasy; the former one occurred when he was asleep (Daniel 7:1). Compare Daniel 8:17-18, where the prophet represents himself as overpowered and falling to the earth because of the vision. The representation would seem to have been made to pass before his mind during the day, when he was fully awake. Compare the case of Balaam: Which saw the vision of the Almighty, falling into a trance, but having his eyes open (Numbers 24:4).

After what appeared to me at first - That occurred in the first year of Belshazzar (Daniel 7:1).