Hi there,
I understand you are in your 12th standard and must be feeling a lot of stress to perform well academically, especially before exams. The important thing now would be to keep a cool mind and plan things out beforehand. You can perhaps start studying in advance and leave only revision for the day before the exam. It is imperative that you try and get a good night's sleep to be fresh for the exam. You can try going to bed by 10.30pm or 11pm the previous night and if sleep still eludes you, you can try to do some deep breathing for relaxing your mind and body, thus helping you sleep faster. I hope this helps you.
All the best.
Next Steps
Plan out a detailed schedule in advance.
Health Tips
Try to keep a calm mind and not lay too much emphasis on your long term future, instead focusing on immediate or short term future