Eli5 why does some pain make us nauseous?

Read the Story

Show Top Comments

If you are in intense pain and your nervous system is in a hyperactive state, while hormones are changing your basic system responses — BP, HR, etc. — it leads to a feeling of nausea. Your brain just has too much going on to process things accurately. Your body is trying to protect itself.


When your body is in extreme pain, your heart rate, breathing rate and blood pressure all increase. These are responses from an involuntary part of your nervous system called the sympathetic nervous system. Evolutionarily speaking, it gets triggers in moments of “danger”. Pain=danger, you’re hurt. Another thing the sympathetic nervous system does is divert blood to organs that need it. Apparently there are parts of the GI system that don’t get as much blood, the stomach especially. The delayed stomach emptying, accumulation of acid and mucus in your stomach, is a very likely cause of nausea. This is likely only one of many contributing factors but I hope this helps explain a bit! EDIT: so I guess the answer to your question is this – some pain makes your more nauseous than other pain, depending on how intensely it triggers the sympathetic nervous system.


I was taught that nerves run through the part of the brain stem that controls vomiting on the way to the brain. When I broke my arm last year I felt intense pain, then felt like vomiting, then the pain subsided to dull aching. So that kind of fits with the overloaded nerves / overloaded brain response


What about getting everything white in front your eyes and nausea? I do attribute it to low blood pressure but sometimes is so random that I think it might be some kind of panic?


As others have stated pain = sympathetic nerve activation. This increases heart rate, blood pressure, heart contractility too. But this isn’t what makes you nauseous. It’s lowering the parasympathetic nervous system which controls gut perfusion and gut motility (movement). The very fast change in this can leave your gut very funny. Nausea can be many things (brain areas and gut) and the nerves in your gut get stimulated after the change in blood perfusion which tells your brain to be nauseous.