i experience physical reactions when i am in a high-rise, or even when i see people skydive or peer over a building on television, but i would not consider it as severe as a phobia. i assume i’m not alone in having curious, indescribable sensations in the legs and chest. what is the physiological cause of these feelings? why is it only in the chest and legs (with the greatest intensity in the calves)?
i’d appreciate a non-speculative medical answer. thanks much.
Well, without knowing you and observing the phenomenon in a lab environment, you’re not going to get an asnwer. I can give you an accurate one, but since you specifically didn’t ask…
What you are describing sounds similar to what I feel when I get an adrenaline rush - in situations where I narrowly avoid a car accident, or I am about to undergo some procedure and am scared. My legs go numb and tingly mostly. Not sure if it’s the same thing as you.
I will specifically ask for your answer.
I think I know exactly what the OP is describing, but I don’t feel it in my chest and calves. I feel it with great intensity in the back of my knees. I can use it as an indication for how high up I am sometimes, because I do feel the sensation even when I have no visual clues of the height. I have had people try to fool my saying wherever I was walking was still ground level, or just barely off the ground, but my knees don’t lie. 
If you don’t experience it, it is hard to describe…at least what I am feeling., It is like when your stomach “drops” on a roller coaster or when you see something shocking, but in the legs instead of the stomach.
So what do you think it is?
I know just what you mean. I call it my ‘flight response’ (as in, fight-or-flight - adreneline is pumping and blood goes to all the limbs in preparation). I don’t even like to see other people around heights.
I would not call myself phobic but I do not like heights. A fear of falling from someplace that will definately hurt or kill you is normal and healthy IMO.
I get the same response when I see people pulling stunts in cars - I know it’s deadly.
Me too, and seeing someone else- even on the television will cause that feeling in the back of my knees. But seeing my kids too close to an edge is the worst. It doesn’t feel like adrenaline though, at least not other adrenaline rushes that I have experienced.
Precisely.
to elaborate, this feeling in my legs (and chest) ONLY occurs when exposed to direct and indirect height stimuli. i know anxiety and i know fight-or-flight and this is different–i’m a psychologist and i don’t have the answer. i don’t want to negate the responses i’ve received, but perhaps i should ask cecil considering the unknown we all seem to experience.
I sometimes have the same feeling in my calves when I’m looking down from heights, or when anticipating pain. I’ve never felt it in my chest. I’m pretty confident this is an anxiety reaction. This kind of muscle pricking feeling is not listed as a part of the fight or flight response, though. (At least not by Wikipedia.) I don’t think this tightness would give you an advantage if you needed to run away from something.
It is an adrenaline/fear reaction. However…
It certainly seems to manifest a bit differently in everyone, and it can easily manifest differently in different circumstances. That’s all.
Would you settle for a very speculative non-medical answer? 
I have a rather severe fear of heights; I can’t ride a ferris wheel, or even walk on some types of bridges. Airplanes don’t bother me … unless I’m sitting next to the emergency door. Sometimes the fear is more a fear of deliberately jumping than a fear of falling.
My fear sensation is not associated with my legs, but I’ll offer a speculation anyway. If there is a fear of deliberate jumping, might not motor cortex be aroused? And if so, might not a sensation seem associated with those “jumping” muscles? (Disclaimer: This is uninformed, totally off-the-wall speculation.)
I get the same response when I see videos of someone undergoing significant trauma.
As mentioned above, it’s basically adrenaline and other stress-hormone mediated, under control of the reflexes and the more ancient and primitive parts of our brains. See danger, prepare for response, whether it be flight, fight, or the need to form blood clots really, really fast.