system
Given the following post, respond as if you're commenting on Reddit:
human
What causes the sensation of one's "blood running cold"?

I got a call from my confused and hysterical girlfriend in the hospital last night, after she gave her head a good crack on the floor, falling down some stairs. The combination of SOMETHING being wrong, but NOT being able to tell me herself because of memory loss/confusion, made me experience the most novel sensation.
The nape of my neck, down and around my shoulders, and some of my back and then down deep deep in my tummy, I simultaneously felt something like a bizarre cool icy stingy feeling. The phrase "my blood ran cold" suddenly made sense. 

Is this side effect of some sort of hormonal stress response? Is it related to the "freeze" response in prey animals? Is the experience of this sensation universally similar?
gpt
When you are acutely stressed your body secretes epinephrine, which activates the sympathetic nervous system that drives the “fight or flight” response. 

Part of that response includes shunting of blood away from *unnecessary* systems to your muscles, lungs, brain, and eyes to help keep you alive in case of a fight or needing to run away. One of these systems that gets less perfusion is your skin, so you may feel cold from the loss of blood flow keeping it warm. The digestive tract also has blood shunted away from it, and it stops moving and digesting food as quickly, so you feel an unusual sensation in your belly.