Do the lessons. All of them.
Do all the quizzes. If you have time check the explanations for them. At least few of them. If you got something wrong or wasn't sure about definitely go over the video explanations though. The quizzes can only help imo…
Take a day off. Or if you feel you need to keep studying more, take few hours off and do something you enjoy. Try to relax a bit. If you have been doing 1 to 3 mistakes and now it is 5 to 7, it could very well be the nerves or burn out or something …
Couldn't have said it better than Dinosaur. Naturally occurring seems to be implied to be the bad kind. This is just an assumption that i am brining in, but going by the word i would assume naturally occurring means just that. Happening in nature. …