The vagus nerve controls many functions in the body, it is composed of 80% afferent nerves. Afferent nerves send signals to the brain about the state of the body, in contrast to efferent nerves which receives signals from the brain. In order for the brain to send signals to our organs it first needs information. This means that a dysfunctional vagus nerve causes the brain to know nothing about how our organgs are working and thus it's unable to send signals to the organs to keep them working efficiently.
Among this functions is digestion. SIBO comes with a lot of digestive issues, but it is often the digestive issues that came first, SIBO just made them worst. When you have a dysfunctional vagus nerve, also known as "low vagal tone", your brain wont be able to receive the signals it needs to ensure that the body is doing a proper digestive process, this means that you wont produce enough gastric acid and as a consequence undigested food will move into the small intestine. This will allow bacteria to proliferate and eventually cause dysbiosis, AKA SIBO.
People with SIBO have a high relapse rate, and this is often because they dont address the source. No SIBO treatment that I know addresses low vagal tone, and for a reason, as unlike for SIBO, fixing low vagal tone it's not a matter of taking pills.
As long as you dont fix you vagus nerve, you will keep having low gastric acid, and other consequences that will cause you to relapse, such as low immune response, an innefficient liver (yes the vagus nerve is important for good liver function) which will not release enough bile to clean up your small intesting, and you will keep relapsing and relapsing no matter how many cycles of antiobiotics or antibacterials you do. Stay tuned as I will be publishing more about the vagus nerve, including some exercises.