A sequel is really the POV character's response to the previous scene played out.
Sequels are the components of your story that deliver the emotional response to what happened in the previous scene. As well as revealing your POV character's thoughts, followed by his/her decision making and thus giving us the next goal-oriented action which leads to a smooth transition into the next action-driven scene. That's the four components of a Sequel wrapped up in a nutshell.
Components of the sequel can be interspersed within a given scene, such as through internalized thoughts (those portions of your manuscript that you italicize), or a sequel can actually play out as a scene of its own. Such as when you have your POV character dialoguing with another character expressing his/her reaction to what happened in a previous scene. Think of the intent of your scene. If it's to provide the sequel components to a previous scene, then you have completed the required follow-up to that scene within a scene and you're ready to move on to the next big disaster-accomplishing scene.
The sequel components, because of their nature, are generally breathers for the reader. They are slower paced and allow the reader to reflect on past events in the story. Because they slow the pace of the story, you would not want to incorporate them into certain scenes. While in other scenes you may find it necessary to add an element or more from the sequel criteria to it. It's up to you as the author to decide on the pacing of your novel, where you want the story to whiz by and where you want it played out in slow motion.
It's the variations of how you get your sequel components (or not) into your story that keep this whole Scene & Sequel concept from becoming formulaic.
Your story and characters really do dictate the flow. If you have a character who is always thinking, then more often than not when in his/her POV you will likely need to mesh the sequel components in with the scene as it is playing out, to show the characterization properly. But remember, even deep thinkers can find themselves in situations where they have no time to internalize or consider the ramification of their actions or discern their next course of action. For those instances a follow-up sequel will be required when the character is ready to express his/her feelings and tackle the consequences of what happened.
When something is obvious, then of course you'll have no need to create a structured four-component sequel that includes the POV character's emotional response, thought process, decision making, and finally the next goal-oriented action. Perhaps only a couple of those components are required, or perhaps none at all, given the specifics of your well-drafted scene. Sometimes what little is required of the sequel components can be interspersed within the acting scene, depending on how fast you want that scene to play out and the feel your going for.
As noted in Scene & Structure by Jack M. Bickham, when structuring your scenes and sequels always be sure to include all the components in one way or another, though. If a component is obvious, then you needed spell it out. You've already incorporated it into your story in a subliminal way and thus your work has already been done. However, if the elements stated are not obvious, it is your job as the author to incorporate all the necessary components in a logical and understandable ordering, to keep your story flowing and to keep the reader's interest. To do this, it may require you to write a sentence, paragraph or even pages of sequel material following a scene, or it may require none at all before heading into the next big scene. It all depends on the individual circumstances of the action-driven scene and your characters as to what is required.
Have fun experimenting with the multitude of permutations of scene and sequel to make your story the best it can be.
On with the fight to write on,