The Baal HaTanya, in his introduction to his Shaar HaYichud V'Emunah, talk about this idea with regards to the verse in Mishlei 24:16,
"For a righteous man can fall seven times and rise".
There he explains that when a Tzaddik advances from one level to another, "Between one level and the next, before he can reach the higher one, he is in a state of decline from his previous level"
The Lessons in Tanya further elaborates:
When one is constantly on the same level, or even when one advances in finite stages from one comparable level to the next, there is no need to abandon one’s former level before establishing one’s foothold on the next; on the contrary, one’s former position may well help one to take the next step upward. When one is truly mobile, however, climbing from one level to an infinitely higher one, his previous level — which is finite compared to the level he is about to attain — actually hinders his progress. Indeed, if he aspires to mature to a more exalted spiritual mindset, he must first purge himself of his previous one.
In a footnote, the Lubavitcher Rebbe explicitly connects this to R' Zeira.
In a Sicha from 6th of Adar, 1980. The Lubavitcher Rebbe interprets it as follows (see there for context):
R. Zeira did not literally forget Talmud Bavli. It was just that this intermission (the period of fasting), compared to the actual learning done previously, is called “forgetting.” And it was precisely this “forgetting” which was necessary to reach the higher level of Talmud Yerushalmi