@dotlin Perhaps you are over doing it. You are practicing so much that you aren’t giving yourself a chance to really relax. If you know the information, you know it. Continuing to practice it isn’t going to make you know it any more, but it will continue to add to your stress. As far as the reaction timing, if you are too tired or stressed out, your reaction times are going to be off. I’d really recommend taking the day before the next test off completely from studying. Take a day to do something you enjoy doing and push the test out of your mind (yes that’s easier said than done, but I think it will help).
If you wanted to take an anti-anxiety medication, you would need to talk to your doctor to get a prescription. While that may work for the short term, in the long term, you need to learn how to control your test anxiety without medication (and taking an anti-anxiety medication could also lower your reaction time, so I would really advise against it).