Studying for an exam the day before it is fruitless (I used to work in exam prep). You already know what you know. Studying today is not going to change anything. You should not berate yourself for not studying today. You need to go outside, have some fresh air, exercise if you can, drink tons of liquid to keep your mental acuity up - those things you need to do. Sleeping and eating are not bad so do not berate yourself for that either. The best thing for you is to be physically active today so that you sleep well the night before the test. The quality of sleep the night before the test is THE most important thing for you.