I'd firstly like everyone who's saying "GCSEs are so easy" to shut up. They're not easy for Year 11s and you're being incredibly unhelpful. Personally, I found my GCSEs more difficult to cope with than my AS Levels.
For all you current Year 11s, you're currently at the hardest part. The mocks are by far the worst part of the year since you've covered most of the content, but your exam technique will still be fairly poor. And of course, this will be your first experience of an intensive exam season. Over the next term, you'll be doing an incredible amount of exam preparation and you'll be given a chance to clarify anything you're not 100% sure about. The actual exam period for me was much less stressful than the mocks, simply because I had the experience of doing it before. Try to calm down, have a restful christmas break, and start revising early. Your school will be giving you kicks up the backside around Easter to revise, but you can get ahead by starting to revise from the February half term. The main problem with GCSEs is the sheer amount of stuff you have to process. Contrary to A Levels where you're expected to have a high level of understanding over a small range of topics, at GCSE you need to know lots of things over a massive range of subjects, many of which you don't like. It's therefore critical that you make clear revision timetables to make sure that you have everything covered.