Good article - Using 'Big T' and 'Little T' for Trauma Can Be a Big Mistake (https://brickelandassociates.com/big-t-little-t-trauma/) by Robyn Brickel, May 2019. Here's a short excerpt:
There Is No Such Thing As "Little Trauma"
Trauma is a fundamental feeling of threat. It's a perceived lack of safety. And it's different for everyone. Trauma is more about the impact than the cause; it's about how the trauma is "remembered" in the body. It is not up to us to judge, or quantify or size up the impact of someone's trauma. The only person who can do that is the person who feels it.
Bullying can be hugely traumatic. Grief can be hugely traumatic. Postpartum depression, anxiety or other mood disorders can be hugely traumatic. Trauma from embarrassment, betrayal and affairs can leave deep, lasting, tremendous impact. These things might be categorized as "Little T"—but there is no such thing as little trauma. Trauma is trauma is trauma!