But with a damaged intuition for the prior probability, my mind didn't successfully >check itself, or even notice a problem - didn't get as far as asking "But what is the >prior probability?"

Ok, but in this case it seems that you took the correct action - don't worry about it - and so it is not clear if this is a valid criticism. Even in terms of application of scarce brainpower, it seems to me that dismissing further worry by means of "low prior probability" is about the same amount of work as dismissing by the likelihood ratio, so once your dreaming mind has started considering the problem, there is no course more optimal than dismissing it and the path taken is not relevant. No?