This is not the reason why I watch this show. This is a mediocre episode.
In this episode, they must fight the urge to sleep. Apparently a bug induces the release of melatonin in the brain. Melatonin is created from serotonin which makes the person sleepy. When you finally sucumb and fall asleep the bug continues to eat the melatonin and eventually it will damage some parts of the brain. This is what killed the people. Also, Vala is being subjucted to a test. This is the only interesting part since she's kinda funny in the episode.
What a total bummer this episode turned out to be. I mean sleeping is their enemy. That's kinda stupid. The only reason this didn't get a lower score is because of Vala. She is totally amazing.