Wally had to give the Speed Force credit, it knew how to put on a show.
Since he got trapped there, endlessly running after saving the Earth from the Reach, he'd seen the course of human history at least five times all the way through, but different every time based on what people did to lead to different timelines. Each time, he practiced looking at a certain part, trying to find what he was looking for.
Every time, he found it. Artemis was safe, but lonely. He never remembered everything, his mind just couldn't comprehend the eternity of time and everything it encompassed. But every time, he saw her, and remembered two important things.
Artemis was safe. Artemis missed him.
This, somehow, gave him strength to continue. The Speed Force, he figured, put his body in suspended animation, so he never had to eat, never had to rest, but if he stopped running, he'd fall out of the Speed Force, into a random place in space and time.
So he kept running, trying to find a timeline where they could help him get out. Trying to find a way to get back to her.