Got a lousy night’s sleep? Feeling kinda grouchy? Turns out waking up on the wrong side of the bed won’t just make you cranky. It will make others seem that way, too. A 2015 study from the UC Berkeley Sleep and Neuroimaging Laboratory found that a single sleepless night can fundamentally alter the way we perceive others—making even the mellowest of fellows seem like the strangest of dangers.