Typically it is said when listening to someone talking-- it is a polite way to let them know that you are paying attention. Think of it as going 'mm' or 'ah'.
There are numerous emotional and physical disorders that have been linked to stress including depression, anxiety, heart attacks, stroke, hypertension, immune system disturbances that increase susceptibility to infections, a host of viral linked disorders ranging from the common cold and herpes to AIDS and certain cancers, as well as autoimmune ...
The effects we are likely to see aren't just trauma from experiencing natural disasters, he added. We can also expect increases in long-term stress and anxiety from the aftermath of disasters, as well as increases in violence and crime rates as a result of higher temperatures or competition for scarce resources..