I wouldn't bank on it. A Levels are so much harder than GCSE's, the jump from GCSE's to A Levels is way bigger than the jump from A Levels to GCSE's. If you're an average student aiming for A*'s in all your A Levels, you will burn yourself out and probably have a breakdown. Schools always inflate predicted grades as they're something to aim for and they boost a student's confidence - you're more likely to work harder if they predict you an A rather than a C because it's the school's way of saying "we think you have the potential to get this grade". It's time to be realistic.
Edit: Please please please never put your education before your health. Getting good grades is important but it's not worth destroying your health as a result. You can get decent enough grades without having to sacrifice sleep etc.