I was watching a movie, and in the middle of it I got an error message, then folders just vanished from the shares. What's going on here? Did one of my drives just die?

How can it be healthy if it just stopped reading from it?

What can I do about this? Is there anything I can do?

Is it too late to save it? Or rather is it too late to save whats on it? Because most stuff on it is really important that I get my hands on again. I'm glad that my password database was accessible still, otherwise I would have probably died there and then.

Next time post the diagnostics, but based on the screenshot, it dropped offline. Power the server down, check/replace its cables, and post the diags after boot.