Hi there! I am currently doing my national 5s and haven’t done highers yet so unsure about that. However, what I can say is that there is no need to be nervous! From what I know GSCEs are similar in terms of knowledge to National 5s. They might vary slightly in content but nothing that wouldn’t be easily picked up if you’ve studied that subject before. You can have a look at the SQA specifications for each subject and have a scroll on BBC bitesize to see what kind of content comes up. In general, the biggest difference between GCSEs and Nat5s is that National 5 is covered in 1 year compared to 2 year long GCSEs if I am correct - which may impact the amount of knowledge that needs to be grasped. Good Luck!