In physiological terms. And also, how to prevent it? I get it a lot and it makes me feel anxious.
Just in case I said it too vague, what causes and what is happening when you get the sinking feeling in your stomach? Thanks
WAG, 12 minutes of work left and with it my internet access, so what the hell, I’ll take a guess 
The fight or flight relfex? Where blood leaves the parts of the body not needed for fighting or running, the digestive tract being one of them. Is this perhaps noticeable as a sinking feeling? So you feel anxious first and this is a symptom of it.
Feel free to correct me.
Is this the same as “Butterflies in your stomach?”
When this happens to me my balls shrink up in my belly and I’m ready for fight or flight. Preferably flight!
Yeah they’re probably the same, something similar is also when your heart sinks. Does some sort of hormone get sent that triggers this reaction?
‘Steven Wright’ (paraphrase).
You know that feeling that you get when you tilt your chair past the point of no return?
I feel that way all the time.
I read somewhere there’s a large system of nerves concentrated in your lower abdomen that responds to emotional states and especially anxiety. Some suppose this is the origin of phrases like “gut feeling” and “visceral response”. This system is not nearly as big as the brain, but it’s still weirdly big and elaborate for a part of the body with no known need for such a structure. Some sort of emotional holdover, perhaps - some animals with small brains have or had smaller pseudobrains set low in the body - nobody’s certain.
I think this feeling is triggered by anxiety, a response to some kind of psychological stress. If you are going through something especially stressful that can cause it. But if you aren’t aware of an outside source, it may be unresolved inner conflict. For example, unacknowledged hatred and rage can manifest this way, often with feelings of guilt that seem to the subject to be clearly tied to some decoy topic that isn’t really the issue.
My semi-educated medical WAG is that it’s probably vagus nerve related and involves the gut and reflex drops in heart rate and blood pressure. At least in some cases. I had that feeling quite strongly once while attached to a heart monitor, and noted that the more I felt it, the lower my heart rate went, until it reached about 40 and I sat down on the floor.
In others, stress hormones like epinephrine and norepinephrine probably cause similar symptoms, even the the physiologic response is elevated heart rate and blood pressure.
Mmmm, interesting points there, when I think about it my stomach dropping, it does. GRAAAH!