It can be a sight, a sound or a scent. And boom, I relive a past experience that was a trauma. It was something that overwhelmed me at the time I was living it, or it was simply too dangerous to reflect on it during its course. Our psyche then stores this event to be dealt with later. And that is the key to healing.
By consciously thinking about a trauma, and discussing it, or writing it down, it loosens its grip on you. I like putting mine in certain places where it happened. It was there. And since I'm not there where it happened any longer, it can't harm me any more. Our emotions, however, trick us into feeling like it is happening now, or not so long ago. Then I must process it, and find the feeling of grief with it. In this grieving lies an opportunity to feel self-compassion, which takes me right back into presence. Mindful presence. Here and now.
My intuition and my instincts then can guide me stronger whenever I perceive a threat to my survival, so it doesn't happen again. Or, a similar situation might make it look like I'm over-reacting, but in fact I'm reacting to the past at the same time. But, like I have written in my book, I have PTSD but I am not it. I am peace at my core.