Jack was aware that Sky had a double personality, but he was unsure if she knew about it, despite her other self telling him not to mention anything to her. Sky's symptoms, however, were very obvious and he couldn't come up with a good excuse to explain to her why she has them. He knew that he couldn't talk to her about another personality, in fear that by revealing something like this, along with her exhaustion and mental pressure her powers gave her, it could cause some serious damage to her mental health. On the other hand, he couldn't explain memory loss, fatigue and exhaustion without a plausible story. He remained silent, until he could find a good answer to her question. Besides, that was what Jade asked too and odds were that she wouldn't want Sky to damage the body they shared, so she would have a reason for asking that.
"Come on, Jack, be resourceful...Sky's health is on the line here. Find something that sounds reasonab...Wait a moment! Sounds, sound...That's it!!" Jack though.
He put his hands on Sky's shoulders and looked her directly in her eyes, to amplify his persuasion.
"I thought that it would be better to keep you uninformed about this, until we figured out a solution. Truth is, Sky, that you indeed fell asleep after us escaping the ship. The events that followed are true, we weren't quarantined immediately after our escape and we did go to a mansion, my mansion. But, in your case, while you were not conscious, your subconsciously used your powers to interact with those around you. It seems like your sound abilities amplify your sensitiveness to your surroundings, making you capable of both interacting with other people and navigating through your environment. I recall you are aware of both of your abilities, since you have already experienced them. I believe that after you get a hang of your powers, you will control them in a degree that doesn't produce this kind of side-effects." Jack replied, without giving any visual sign of lying.
He then thought that the others couldn't possibly come up with the exact same story, so he continued in a joking tone:
"By the way, you were sleeptalking, sometimes not making sense. You called me Bob once and I kinda felt like a truck-driver on a highway, listening to country music. You even gave yourself another name once. So don't think too deeply if somebody calls you Jade or something similar. He will be teasing you!"