Last I checked, the FBI aren't in the medical field. That buck stops with the candidate who received medical treatment.
I wasn't alive for Reagan's assassination attempt, but from reading about it and family who were alive at the time discussing it, he was transparent. We heard from the docs, we knew the details straight from them in a way that we just haven't here.
You can go ahead and think it's nothing, fall back on "I saw what I saw on the video", but if someone wants this particular job, I expect a lot more.