Not understanding the differences between humour and person being serious. Then overreacting

Hi 

I get really confused with what is suppose to be a joke or when someone being serious.  This has happen on many occasions in my life and I have ended up overreacting and this often coming out in emails and then hours later regret it simply because I misunderstood.  I have end up upsetting people. Its like don't think and I obsess on the littlest of things a person has said and later realize I was in the wrong. 

Has one else experience this?  I was wondering if anyone has any advice as I feel I am lost translations sometimes.