There is one excellent book I know of that teaches this, "Whatever Arises, Love That," by Matt Kahn. This is all "spiritual" stuff and may or may not appeal to people, but it works. And, in addition to helping one's trading this work can also help in life! (Not reacting, release fears, anger, etc.)
The concept is that you don't even need to know where these feelings originated (probably from a childhood trauma). The body remembers, so when you clear the feelings from the body they are gone. Talk therapy has typically spent a lot of time talking about the issues, when all we really need to do is feel them and let them release.