When someone who’s generally healthy feels bad, they can usually tell you why: they drank too much last night, they haven’t been sleeping enough, they’re under a lot of stress, they’re getting sick.

When you have a chronic illness, it isn’t always so clear.

I was doing unusually well over the last few weeks. I wasn’t feeling as good as I do in the fall and winter, but as far as summer goes, my pain and fatigue and other symptoms weren’t too bad.

Then I started feeling unusually bad. I was more fatigued. I was depressed. I was in more pain. The symptoms ebbed and flowed but were always around. What happened?

I weighed the possibilities:

• Maybe it’s the weather. But I’ve been staying in air conditioning. And it’s hot and humid, but not nearly as bad as it was last week. There’s no reason I should feel so much…