There have probably been days when, after a sleepless night, we have been rather unsympathetic to the world around us. In principle, this comes as no surprise - after all, we need sleep to rest, so we may simply not feel well when we are sleep deprived. Much is already known about the impact of insomnia on health, but specialists at Sweden's Karolinska Institutetdecided to take a closer look at how it might be related to emotions .