I think you are doing the right thing by investigating whatever might be causing problems. You either rule it out and breathe easier (and keep looking!) or you identify something you can then deal with.
As for the vestibular thing and not looking so bad...that is totally possible. That he never really LOOKED bad to you. It's common for parents to NOT notice the signs that I do as an OT. I'll have parents tell me that their child is very strong but then I see hypotonia and weakness all over. The reason parents don't see it is because children are intrinsically driven to succeed at things, development to task mastery. But when a particular task is hard the child will sometimes skip it. Crawling is a good example. For a child with poor trunk tone and low postural stability, you can walk easier than crawl, because crawling requires a certain amount of stability - it is a slow form of mobility. But if you just lock your hips and legs and keep moving, voila, walking! Even with low muscle tone! And by skipping a hands/knees crawling phase the central nervous system loses out on some pretty important sensory input necessary for development.
And when others in the family experience the same thing, then the "symptoms", if you want to call them that, look okay. Because others in the family are the same. I have mild vestibular dysfunction (I call it motion sickness!) but my kids escaped - they can read for hours in the car and never get sick. But a lot of parents tell me they are the same as their child. I'm sure there must be a genetic component, though one has not been identified. No one really knows why it happens. Jean Ayres just theorized that some people are hard-wired differently.
I don't think that the actual SID is getting worse. I think the presentation is worse. As Mite has to meet more difficult challenges and he is unable to compensate using his intellect, then tasks are showing up as being more difficult. I see this a lot. I get children referred to me at the age of 8-10 years who have never even been identified as having SI disorder or even any particular problem. And the presentation is just so obvious to me. It's just knowing what to look for.
I hope the testing goes well for all. Hopefully anything that turns up will open doors to answers. I'm sorry for your distress and certainly empathize as both an OT and a parent. Hang in there! You are moving in the right direction.
