“Get busy living or get busy dying.” - Ellis Boyd “Red” Redding (played by Morgan Freeman in The Shawshank Redemption)
I've had this conversation with my own therapist, and other therapists that I know over the years. It is a form of anxiety: "oh, no, I'll forget to be productive."
According to them, it is VERY common in engineers, apparently. Perhaps because of technology's rapid pace? Personally, I was able to control this little demon of a thought by looking at my entire life OUTSIDE of work, and how I simply can't stop learning: I do it constantly, I'm always picking up new things to try when I'm bored, and I revisit the same things at larger epicycles (know how many times I've picked up a big C++ project since the 90's, just for fun?)