The important thing to remember is that the way you feel is normal. Not going is the rational thing to do given the way you feel.  If you had gone on with your trip in spit of how you felt you would have been acting in an irrational way. 

All many people in the US are doing is getting to grips with a different form of risk assessment.  For me it is no longer a factor as I haved lived in London on and off for the last 25 years.  I do remember deciding not to go into the center of London after one of the bigger bombs some years back but I would not make the same decision today.

ShaunP.