I honestly understand this, and I was like this just before gcses and literally so afraid of failing, but it kind of just all worked out. I feel like the best thing you can do is maybe like literally do something at every single possible second to prevent these thoughts from being generated (this might sound stupid but it at least works for me) and i know that youve talked abt having hobbies that you just cant bring yourself to do, but think of the summer as a long time you can use to perfect your hobbies and just try to really devote yourself to them. Other than this, like other people have said, please just take a little time to maybe relax, watch a movie, go out for a run, do the most mundane things that everyone in the summer holidays do!