I was watching a podcast the other day and the placebo of sleep was mentioned. I looked up the Study and also found this article from The Atlantic.
It appears knowing or acknowledging you are tired creates lethargy. Someone telling you that you had more sleep improved brain functioning tests. We believe the lies. The implications are that when you keep telling people how little sleep you got or how tired you are, you are essentially creating even more environment for lethargy.
Just like when you are tired and your coach told you to never show it, get your hands off your knees, stand up. Act like you have energy, seems to have merit.
Don't say you are tired, don't act tired.