Not having seen a doctor for over 35 years I tended to think of MSG "poisoning" as mostly in the mind, a bit like a decade or so ago everybody developed RSI
Then one day walking around the block I felt terrible and had to go home. I felt like vomiting (I never do...) had a huge headache ( again never happens with me) and felt like I also had the runs. That lasted about 30 min. So I went to bed .Slept for a few hours and upon waking up all of the symptoms were gone. That happened again at work (I thought that I was going to soil myself coming home, a short trip at that) and a few days later at home. Finally I figured out that on those three occasions I had some vegetable spread that some friends had given me. So I Googled that spread and "reaction" and MSG came up.
Turns out that as long as the MSG part of the extract is less than 50% it can be called "flavouring/extract/vegetable enhancer" or other such names.
So Vegemite,Promite,Marmite and other yeast/vegetable extracts are full of it.
Stock cubes and some "cup a soup" type foods have a lot of it. (some occurring naturally, hence the "no added MSG" label)
BTW THE so called secret ingredient in the KFC "secret herbs and spices" (not the original,the stuff they use now...) is Accent, and that is mostly MSG and salt

Franco