What you've described is very similar to my own experience. When my reality changes, I also feel that what I am experiencing in that moment is absolutely what I think, feel, and believe. I also think my perceptions are correct.

But then later (anywhere from a few seconds or a few hours), I will go back to what I would describe as my normal state of mind, with my usual thoughts, feelings, and beliefs.

Then I look back and think, "What was I doing? Why did I say that?" Because my actions at that time were not typical of the way I usually am, it felt like "not me."

My understanding is that drastically altered thoughts, feelings, and perceptions (especially if they are transitory and don't represent our usual self) are symptoms of dissociation.

It's good that you've begun to notice when this happens to you. You are beginning to recognize when your reality changes, and you experience both sides of your reality at the same time (not sure how else to say it). This is how it happens for me as well.

I've recently been diagnosed with co-conscious DID, but that may not the case with you. Dissociation is a feature of other disorders too, such as BPD, C-PTSD, and DDNOS.

I'm glad you are communicating with your therapist about what you are experiencing. This will help them determine the best way to work with you toward healing.