Rashi: I was sleeping in Nevu'ah of punishments. In this Nevu'ah, I woke from my sleep. Radak - most Nevi'im receive Nevu'ah in dreams.

Radak citing Targum Yonasan: On the tidings of the future days of consolation to come, I woke.

Radak: The Vov is like the Vov in "Atah Katzafta v'Necheta" (Yeshayah 64:4)- we already sinned, therefore You became angry. Also here, I woke because I already saw consolation in this prophetic dream, and amidst it I woke and rejoiced. When I returned [to sleep] afterwards, my sleep was pleasant to me, amidst Simchah - the opposite of "u'Shenaso Nihyasah Alav" (Daniel 2:1).

Malbim: Yirmeyah could not see Nevu'ah while awake. Since he had great pain, for he always saw punishments, Ru'ach [ha'Kodesh] did not dwell on him while awake, only in a dream. Then he saw his Nevu'os, and his sleep was always disturbed and frightened from confounding visions. This Nevu'ah was an exception. I saw it while awake. (It is a higher level than Nevu'ah in a dream.)

Rashi: It was pleasant [Malbim - because my sleep was not stolen ¹ ].