Pain just feels so dis-jointed from the rest of the episodes, like the lost episode that they forgot about, got to 19 episodes filmed, and went back to make up the quota, people would have screamed 'filler' if they had done a whole episode in the void? Guess what, they're screaming 'filler' at Pain because it feels like more of a slap in the space in that they've spent 2/3 episodes setting up a pretty large event in the lives of these people we're supposed to be getting invested in, and then dismiss it without so much as a expositional piece of dialogue.
This would have been MUCH better being set during the void, at least then the whole thing of them being in the void could have been a mis-direct while they try to figure out what's causing people to be affected by the hallucinations, it could have been explained away that the ticks were hatched from eggs on some fruit that they had stored or something like that to explain why no one was affected until they were part way through the void.
You don't setup something like the travel between galaxies and then dismiss it, it's poor writing, especially when it's on a show that's trying to establish continuity and not have stand alone episodes.
I'm curious to know the production order this episode was filmed in, as i said, it feels like the episode was tacked on to make up the 20 episode season order and they run out of ideas (and maybe because of Huffman's progress at the time they decided they couldnt place the episode earlier in the season? - in which case a good writer can cover that up).