Blame the amygdala.

Huffington Post has a piece on how people with anxiety have mappable brain differences.

The cited study found that: "people diagnosed with anxiety are less likely to be able to differentiate neutral or "safe" stimuli from threatening ones." Which, I mean, like, duh. A bit more:

The scientists found that those with anxiety experienced lasting plasticity long after an emotional experience (aka a "stimulus") ended. This means the brain was unable to distinguish new, irrelevant situations from something that's familiar or non-threatening, resulting in anxiety. In other words, anxious individuals tend to over-generalize emotional experiences, whether they are threatening or not. 

Most importantly, researchers noted, this reaction is not something that an anxious individual can control, because it's a fundamental brain difference.

Apparently they found that the participants with anxiety has differences in the amygdala, which is associated with fear.

         * Pop-culture aside: amygdala makes me think of medulla-oblongata. *

Anyway, the piece goes on to say that an emotional event can induce brain changes that can then lead to "full-blown anxiety." It seems like something becomes unable to distinguish a given stimulation from something dangerous.

The new research is a sound reminder that a person is hardly responsible for having a mental illness; surmounting evidence shows mental health conditions have genetic and physiological underpinnings. A 2015 study found that anxiety may be hereditary, while other research suggests depression may be an inflammatory disease.

I hope research gets more funding, because something tells me we're so close to a breakthrough in treating depression and anxiety. There's a major missing link, in this "modern plague."