I'm glad you said that. If you feel comfortable doing so, could you share an anecdote? If a few people describe this from different angles perhaps more will come out of the woodwork and offer some solutions.
I think the person you were replying to was gently suggesting to see a psychiatrist.
Not sure how relevant it is, but I've also had to retake multiple theory courses in my time at school so far. Calculus, linear algebra, discreet structures.
In terms of seeking professional help, I'm seeking some myself this week, though admittedly for social and general anxiety (related or not to my productivity, I'm not sure).
https://en.wikipedia.org/wiki/Analysis_paralysis
The way out of it is just to pick something and see how far it takes you, accepting that you may have to backtrack and redo stuff in the future. There's this myth that experts got that way through good decisions; no, usually experts got that way because they made a lot of bad decisions really quickly and dealt with the consequences, and so now they know not to make them again.
Let's go to the redoubtable Yegge and his concept of "Shit's Easy Syndrome":
http://steve-yegge.blogspot.com/2009/04/have-you-ever-legali...
Stick with it. The set-up is long, but it pays off handsomely.