Whenever I look up diseases and it reports a statistic such as "3-5%" I often feel like either I must not be interpreting it correctly, or it is so region-biased as to not be useful for how I'm consuming the data. Because it's hard to reconcile that apparently in the ballpark of 1 in 20 people have this?

It seems extremely common as people age. Your body just starts to break down as we get older and this is one, amongst many, ways that this manifests. A quick search suggests it shows up in about 50% of people over 70. [1]

[1] - https://pmc.ncbi.nlm.nih.gov/articles/PMC11879357/

Lot of these are a spectrum. 3 to 5% might have a mild form that's aggravated by super spicy food or something but otherwise not very noticeable.

And then maybe a percentage of those people have a more debilitating version ?