That's very surprising that something bad happened with as low as 50mcg (2000 IU). I was suggested to take that much by my doctor _daily_ without even bothering with a test (granted I'd taken a test years prior in a similar climate, perhaps that was enough for him). I even temporarily upped it for a period to 4000 IU basically for the same reason as you. And I think I've heard some people claim that as much as 5000 IU is safe without a test?

It's just surprising that this happened to you given that you're naturally deficient.