You only feel useless but don’t think for a moment that you lost that knowledge or experience.
It’s amazing how the brain stores these things - they seem lost but just a refresher will bring them back.
Breaks are good whether they are forced or not.
For example, I studied lots of math in University about 20 years ago and mostly forgot all of it because my life took a different path and I didn’t apply any of these concepts. Lately I started reading some of those mathematical concepts again and I understood them more easily than I would have if I had never seen them before, even though I had forgotten them. Anything you learn you can easily forget but your brain will generally have an easier time relearning it again. Like you, I sometimes read code I wrote several weeks or months ago and it looks strange at first, but it comes back to me after a few re-reads. This is a good example of why comments in code are so important.
Keep at it and good luck!