Good read, I can advice to learn how to behave in those situations, the majority of the people are not ready for such an event because they never had to live fearing something like that could happen. There are many guides and books on how to be ready and what to do in the unlucky event that an attack happens around you, the simple rules that I know are:

1. Know where the nearest exit is.
2. Keep your eyes around and focus on suspect people.
3. Keep in mind good covers like tables, walls or anything that will save you from bullets or explosive fragments.

Stay strong!