I'm scared that I messed up my English exam - the only subject I've ever truly loved and I want to take it to university, so I completely understand how freaked out you're getting. It's hard to get the thought of failure out of my head. But it's also important to not let it drag you down. There are more exams to come, and it's not the end of the world, there's always retakes and hey - you might not have done as bad as think!
You have to make sure you're looking after yourself though, stay positive, get as much sleep as you can and eat properly. I've found it helpful to talk to my subject tutors - they're generally really encouraging and reassuring. Don't let the fear of results spoil your summer either! Good luck x