Two days ago, I felt a little under the weather and thought I was coming down with something. I went home that evening feeling cold. I took my temperature when I got home, and found out that I had a fever, so after having a nice bowl of chicken soup, I went straight to bed. I slept well and woke up feeling much better.
I felt fine all day yesterday except for a slight sore throat. I thought surely, the worst was over and that I was getting better. Unfortunately, I woke up this morning with my throat feeling worse and my voice sounding horrible. Fortunately though, I don't feel under the weather anymore, and I definitely don't think I'm coming down with something. As I told my students, my voice sounds horrible, but I feel fine.
You say you're coming down with something when you're beginning to feel horrible and you're about to get sick. When you're already sick, you can use the past tense: I came down with something.
A: How's Susan? I heard that she came down with something.
B: Yeah, she was feeling under the weather yesterday. Now she's at home with a high fever.
A: That's horrible. Everyone's getting sick these days. We're just passing it on to each other.
B: I know. I usually take extra doses of vitamin C whenever I feel like I'm coming down with something.
A: I drink lots of orange juice and get plenty of rest.
under the weather - feeling sick or very tired (see yesterday's blog)
about to - almost going to happen (see the May 27, 2009 blog)
dose - amount or strength of medication or vitamins
Being under the weather and coming down with something are very similar. However, being under the weather can simply mean you're extremely tired, while coming down with something specifically means you're getting sick. You can also be specific and say she came down with the flu or he came down with a cold.
Stay healthy, everyone, and have a happy Thanksgiving!