1. Do Meditation and breathing technique 15 min before test.
2. Do know there is no bad consequences in any circumstances whether you pass or fail.
3. Listen to motivational recorded voice of yours indicating you past achievements.
4. You may try herbal remedies like chamomile in the morning before test instead of coffee or tea.
5. Last but not least, if you could get support you should do that; e.g. talking to a family member or friend.
Cope with chronic illness
https://meempowerme.com/2022/04/29/chronic-illness-invisible-disabilities/