It seems you can have a reaction that is, in effect, a reaction to a reaction as in Sam’s MRUs taken from Advanced Fiction Writing's Blog.
This is good so far, but now you’re worried about the sentence that follows: “The all too familiar agita churned.” This is an emotive Reaction, but what is it reacting to?The answer is that it’s reacting to the POV character’s own interior monologue. So it has to come after the interior monologue. You’ve got the emotive response in the only place it’ll work.
Interior monologue being a potential rational thought and therefore a potential reaction in itself.
I've been struggling myself with the fact that it must be possible for the protagonist to react to internal thought. For instance, remembering something important that they had forgotten to do.
Seems only logical. Well, some of the parts of the information, in the articles, I've posted about obviously stuck with me more than other parts.
I've quoted this before, but see the important stuff about being a beginner? Well that's me. I'll have to try and keep the protagonist out of the Motivations but where he is in there I'll have to extra vigilant it doesn't end up being a mix of Motivation and Reaction.
Most important of all is the fact that your character does not appear anywhere in the sentence, either by noun or pronoun. This is especially true while you're still a beginner, getting the feel of this device. For example, you do not fall into the trap of writing, “Now, Brad saw the red Jag pick up speed,” etc. The reason you shouldn’t do this is that it’s very, very easy for the inclusion of any mention of your character in a motivating sentence to transform said sentence into one of reaction; or, at least, to mix the whole thing up to the point where there’s a feeling of clutter to your sentence.
Dwight V Swain