Glad you are feeling better, Emily. I get this warning of illness in the same way! Like, I was ready to throw my bike down 2 Sundays ago, even though I had been sick Friday and my body was just telling me I wasn't really better. I think I willed it out of me so I was fine for the hard riding in the Berkshires, because I had a slight replay of it all when I rode Wednesday and Thursday. Slight, though. The gym was fine today and I will do a hard ride tomorrow.
You are smart to listen to your body. I did not do this in my 30s and 40s/early 50s and I think it set me up for a lot of stuff that was my own fault. I have a terrible fear of having to slow down (overall, not just my speed), but I am not in the mind set to do this in the foreseeable future. I think my upcoming birthday in the fall (65) is scaring me more than I like!
We went to the outing, ate our lunch, had half a beer, and left. DH had no desire to do any of the activities, either. Instead, we got our grocery shopping done and went to the local farm, so we can do a long ride tomorrow.