Here is a nice article by Lisa Brookes Kift on her blog at LisaKiftTherapy.com:
We all seek happiness. We all want to feel calm, grounded and avoid being hijacked by our own emotional reactivity. Thankfully, the recent studies in neuroscience are demonstrating how to do this. If you find yourself easily stressed, worried and fearful, there are likely personal historical reason for this when your brain learned to be extra vigilant.
For example, if you had experiences of not being included in childhood, you may have a sensitivity to being left out of group situations or feeling invisible now. These types of situations may feel pretty big and painful to you! This is because your alarm center in your brain (the amygdala) has been trained to respond to this particular trigger. There are countless other sensitivities people carry such as fears of not being good enough, safe enough or in some cases, lovable at all.