How just THINKING you've had a good night's sleep can help you function better

Feeling tired after a bad night's sleep?
The good news is that simply being told you've slept well could help perk you up.  The phenomenon - coined placebo sleep - involves telling people they've been in a deep sleep even when they haven't. 
Students who were told they got a good night’s sleep performed better on tests measuring their attention and memory skills than those who thought they slept poorly.
Researchers at Colorado College in the U.S. devised a ruse in which students were told that a new technique – which doesn’t actually exist – could measure their sleep quality from the night before. They were connected to a machine that measured brainwave frequency and shown dense spreadsheets and formulas. 
Some were informed that their deep, or REM, sleep had been above average the night before, a sign that they were mentally alert.

Source  - Daily Mail