I found that there isn't as much variety in complaints as you would expect if people were independently making things up to complain about and there isn't as much consistency as you would expect if the complaints were due to social contagion.
There does seem to be spikes around general awareness like when a popular TikTok or famous person is diagnosed with a thing, but it's possible to use the less well known bucket of comorbidities to figure out what percentage of those are examples of social contagion, what percentage do present with these actual conditions, and what percentages are true hypochondriacs. The first group lack the depth of comorbidities that the second group have, and the true hypochondriacs tend to claim they have absolutely everything no matter how preposterous.
From what I found the large majority of those considered hypochondriacs do exhibit the conditions that they believe they have. The social contagion and true hypochondriacs appear to cooccur with mental disorders and are only a small percentage of the cases. I really wish medicine made an effort to distinguish between these three cases to extract the apparent hypochondriacs from the true hypochondriacs and treat them separately.
I think a large number of those with undiagnosed conditions actually exhibit conditions from the hEDS bucket of comorbidities which is especially vast and varied. See https://ohtwist.com/about-eds/comorbidities for an incomplete list. This bucket does include SIBO. So if you have been told by a doctor that you're a hypochondriac and you exhibit SIBO these do increase the probability of you having hEDS. There is an assumption that hEDS requires the person to exhibit excess flexibility and while this does appear to be generally true it doesn't appear to be a necessary condition. A person with hEDS, especially if they are male, may not exhibit any excess flexibility but will exhibit hEDS comorbidities at the exactly same rate as someone who has been officially diagnosed with hEDS which would be rather unlikely if they didn't have also have hEDS. Of course if a person exhibits excess flexibility that would increase their likelihood of having hEDS. What is very unorthodox about about my view is that this flexibility is not an essential component so a lack of flexibility is not sufficient to rule it out even if it does reduce the likelihood.