It means he was almost completely removed from all physical pleasures and from this temporary physical world. He only came out of the cave daily to get a small amount of food fron a tree growing right outside the cave and went directly back inside to continue learning Torah with his son Rav Eliezer and be completely attached to Hashem and learning Torah all the time.
During his stay in the cave he put together the Zohar of Kabbala which we still have today boruch Hashem but is only safe for certain tzaddikim on a very high level to learn.
May we all start working on ourselves on our dveikus/attachment to Hashem full time which is a direct mitzvah straight from the Torah “u’lidovka boi”