It is widely believed that trauma in the body happens when your central nervous system gets stuck in fight, flight freeze or fawn mode and creates a lasting emotional wound.  If that emotion is re-triggered you can experience instant outbursts.  This can lead to overthinking, head pain and anxious sensations in the body.  Traumatic events can be one event like receiving or witnessing physical or verbal abuse or ongoing subtle events like emotional unavailability, gaslighting or narcissism.  Also what may be traumatic for one person may not be for another.  Even something small that wasn’t resolved, apologised or reassured properly might affect us in adulthood.  

You can experience trauma at any time in life but it is believed that the formative years of childhood creates the most opportunity for trauma to create emotional wounds as we are still developing and also we can often not escape or fight so the freeze or fawn mode is often activated.  

Check out these two articles from Psychology Today for more information on overthinking  and childhood trauma.