A quick update:
I really appreciate the kind words and comments. I think a big part of the problem is that I have looked absolutely awful the last several days, which I only realized because one or two more senior people said something to me today. I have also been really grumpy but had been trying hard not to show it or take it out on anyone (which is probably why I looked so bad, too). I am feeling better today for various reasons, so I have not had nearly as many comments or offers of help. So, I will keep up with moving around/hydrating and will try to give a general "I'm fine, thanks for asking!" kind of response. And I will certainly be thankful for my wonderful coworkers.