I was sick several days this past week or so. Or maybe it was just a delayed reaction to my booster shot. There’s no way to know.

I got my Covid booster on Thursday last week, and my initial reaction was pretty minor—the injection site was mildly sore for about three days.

On Monday this week I met with my Esperanto group as usual, and went with Jackie to her x-ray, post-surgical consult, and physical therapy appointments on Tuesday, also as usual. I’d felt fine in the morning, and we’d made a plan to go out to lunch, but by the end of the physical therapy appointment I was starting to feel crappy, and said I wasn’t up to lunch out.

That night I spiked a fever of 100.2℉, and had the usual body aches that go with a fever.

I didn’t start coughing, so I figured it probably wasn’t Covid, but out of courtesy to my fellow Esperanto group members, I sent email the next morning letting them know about my fever.

I felt some better most of the day on Wednesday, but then felt much worse Wednesday evening.

That night my fever spiked up to 102.9℉. Still no cough though. In fact, no other symptoms—no sore throat, no stuffy nose, no nausea. Just a fever.

With that high of a fever, I figured I should probably get a Covid test, so I did that Thursday morning, and otherwise just rested.

My Covid test came back negative, which was reassuring, but still left me wondering what the heck it was.

I woke up Friday morning feeling almost entirely well. My Oura ring reported that I still had a upward overnight temperature deviation, but my implied fever was just 99.8℉.

I’d planned a day trip with friends on Friday, but figured I had to cancel that. I spent another day just resting, although I basically felt fine.

Today I again feel fine. My overnight temperature is back down to baseline.

I have to say that I’m pretty pleased to have this temperature data from my Oura ring. It has been very handy. Looking back over three years of data, I can see one other temperature spike almost this large, from another day when I was sick, and smaller temperature spikes when I’ve had vaccines of one type or another (two shingles, three flu vaccines, and my two previous Covid shots).

As I say, I’m feeling fine today, but one other metric that I pay attention to is not yet back to baseline: My resting heart rate.

My resting heart rate has done a very good job of indicated whether I’m ready for vigorous activity, and the current level suggests that I’m really not.

So I’ll take it easy again today. Do my morning exercises. Maybe get in a little walk.

I’ve documented all this primarily as a record for myself, so I can look back and remember what happened on which days. I’m still in the dark about what was going on, though. Presumably not Covid, based on the negative test. Maybe the flu? (I got my flu shot in early October, but it’s not nearly as efficacious as the Covid shot, so catching the flu and feeling crappy for a few days is entirely possible.) Maybe some other virus?

Or maybe it’s just an unusually delayed reaction to my Covid booster.

I guess I’ll have to live with the question.