Character development – Types of Physical Responses Part 1 of 5

In the interest of developing characters that react to situations and feelings uniquely, I have come up with five different types of physical responses.

1st Undetectable Responses
2nd Involuntary Outward Responses
3rd Subconscious Movements
4th Conscious Movements
5th Verbal

This post will deal with the first.

UNDETECTABLE RESPONSES

Undetectable responses are reactions we have internally that are not visually evident to those around us. Only your Point of View character(s) will ever experience this type of response.

~ Butterflies in the heart or stomach
~ Pulse quickening
~ Ringing in Ears
~ Sudden tunnel vision
~ Migraines

These are all examples of physical responses that are only known to the person experiencing them.

I occasionally get a headache when I am really stressed. While this physical response to stress is painfully evident to me, it's undetectable by anyone else.

What are examples of undetectable responses you have?