Thought/feeling relationship

The model often gives me such good insight, but sometimes I cannot hear the thought causing the feeling at all.

For example, I was in the middle of a task at work that requires a reasonable amount of concentration, and I was focused in on it. I became gradually aware of a rising feeling of sadness. I was in watcher mode, observing the sadness become more intense. All my thoughts had been focused on this work task, and none seemed connected with the sadness itself. I continued to work on the task until it was complete. I could not detect a thought that had been causing me to feel sad. The feeling of sadness ebbed and flowed throughout the day.

I also have this happen sometimes with other feelings, such as happiness, when I suddenly feel a great sense of happiness without any precipitating thought or event.

When an emotion presents itself in this way and is not linked to a thought, does that indicate that it’s actually a sensation (i.e. a biochemical change) that isn’t caused by a thought? Or can you offer me some other way to make sense of this? Thanks!