Think you're fully alert? You can't always tell if you're tired

How safe is it to drive when you haven’t had much sleep? Just like drinking alcohol, it turns out we’re not always a good judge of how mentally affected we are.

In an experiment where people were only allowed to sleep for just five hours a night, for a month, people did not realise that they had become less vigilant.

“You’re asking the sleepy brain to tell us how well it is doing,” says Elizabeth Klerman of Brigham and Women’s Hospital in Boston.…