I've only managed to see this episode once, but something I didn't understand was Spock's decision to try and hide in the debris field. At this point they believed the planet was the source of the problem, but it seemed mostly a guess that the debris field might shield them.
Wouldn't the most logical action have been to get as far away from the planet as reasonably possible until the effects appeared to subside? I know Una made a point that they had crew down there, but it's not as if they can't return more cautiously and with a clearer understanding of what's happening. You're also helpless to help your landing party if you're completely incapacitated yourself.
Have I missed something important?
It's been a while since I've seen TNG and maybe my memory's bad, but the first one that came to mind, Data's Day, seems to be one that nobody's yet listed.