Have also had a lot of low-grade symptoms - very sleepy all the time; waking up exhausted; itchy, runny nose; sore/stiff/weak joints; dizziness; strange confused headache; and yesterday my vocal chords felt all overstretched, which is a really strange feeling. These are all symptoms of the chronic hyperventilation, which right now is probably occurring because of the itchy, runny nose (it's hard to breathe properly if you're all snotty), which is probably a cold manifesting just in my nose and chest, or allergies, or both.
None of this is very surprising given the time of year, but I don't like having a head stuffed full of cotton wool, and I especially don't like not being able to concentrate for more than 5 minutes at a time. Bleargh. Now I'm going to shut down all other windows in an attempt to focus my scattered thoughts, and try to write down my current plot dilemma so people can give me advice on it. And hope I don't completely lose my ability to do coherent English in the meantime.