Ever find yourself exhausted despite not physically working hard? Whether it is thinking about what to eat, what to wear or remembering to put your phone on charge -- from the moment we wake up modern day life is filled with decisions. Although these simple choices may not feel like strenuous tasks, studies suggest they could be overloading our brains and making us tired all the time. In fact, by the end of a day filled with seemingly minor cognitive tasks we may find it even harder to make rational decisions, and experts say a build up of a specific brain chemical could be to blame. Here, MailOnline reveals why decision fatigue really is making us all exhausted.