[InTheSwiss]

I have been on Ambien (Zolpidem here in the UK) for 5 years now after being diagnosed with insomnia due to PTSD (actually diagnosed by three doctors at a psychiatric hospital where I had to spend 4 months in 2009 not some self-diagnosis) and I am not too sure on this evidence. I know a lot of people who suffer true insomnia (as in doing several days with perhaps 15 minutes sleep) and thinking you got good sleep does not make up for the fact that you are actually going several days with awful sleep. I am sure there is some kind of psychosomatic side that makes you perform better because you think you will but suffering real lack of sleep cannot be "tricked" better with positive thinking just like how depression cannot be fixed by just "thinking happy".

[carbocation]

The study population was undergrad students, not insomniacs (I mean, maybe self-styled, but you know what I mean). Therefore, you're probably right that this finding might not generalize to a distinct population with disordered sleep. But for the typical HN reader, it might be of more interest.