I dunno if I'd call what Ensign Rager looked like awake. Eyes open sure, but more like anesthetized. Riker had to carry her out. She was down from something, something he wasn't down from this time, because Bev had given him stims.Problem is, they were awake when they were over there. Otherwise, Riker wouldn't have been so tired afterward.
The thing is, everyone did have memories, foggy, latent, subconscious even, but memories. It was very much like those you'd have from partial sedation or some beginning/ending state of anesthesia, & none of the memories were of the experiments done to them, like Riker's arm removal. I mean if it was a memory wipe, it was a pretty terrible one, that left a LOT of traces, & it would seem unlikely if they were so alien, that they'd even know how to do one on an alien being, but if it were generalized sedation, then it would explain how they remember some stuff, but not all of what happened.
The only thing needed for Riker to be tired is a disruption of REM sleep, which some types of anesthesia might do, especially alien in nature. When he rescues Rager, she has some tubes mainlined into her arm that he has to detach. My general assumption was they just pumped some kind of sedative into them, & did awful things while they were under.