When you picture yourself in a situation from your past or take it from your imagination, your mental and emotional state shifts from the state of relative comfort to the one reflecting the chosen situation. Now, when you want to ruin the same situation again so you can notice the very beginning of the emotional shift, you absolutely must let go of that situation and ensure that your mental and emotional states return to the original state of comfort. In fact, the greater the feeling of comfort you can reproduce, the clearer will be the shift back to the emotional reaction that you chose to examine or shut down.
If you don’t let go of the emotion completely before you imagine it again, the sensations that comprise that emotion won’t become turned off. As a result, when you recall the situation again, you won’t feel it appearing in your chest. What you’ll feel is spilling of that emotion to other areas of your body, such as the throat.
I hope this explanation isn’t confusing.