In addition to the suggestions already made:
1. Getting out of the rut: Some people find that boosting confidence and having a series of positive experiences with testing drastically reduces test anxiety. If this sounds like it would help, you can try to find a coach (sports coach style) to motivate and encourage you or a hypnotist for guided meditation/hypnosis, or an awesome tutor or peer who can motivate and encourage others. The internet is an excellent way of finding all of these, and in fact, I know people who have found all of those on the internet. Online there are some excellent videos that sum up most gen chem and biology topics very well. (Recommending specific businesses is considered against TOS by some of the mods on here, so that's why I'm being vague.) If anxiety is new to you, think back to before you had test anxiety and you felt back then prior to tests.
2. Cleansing chemical soup: Get your body out of panic mode (if it's there) and into a relaxed confident state overall. Staying away from things that provide the similar sensations to test anxiety is a start. For example, if tests and scary movies make you feel similar, stay away from scary movies. Instead, try to surround yourself with things that set your overall emotional/physiological state to where you want it for the test. Exercise helps too. Do some of your homework while on the elliptical or treadmill in the gym if possible. Just don't overdo the exercise or you might suffer fatigue, as you may or may not already know.
3. Vent: If you have thoughts that increase the anxiety, find a supportive person to share those thoughts with. Many people find that venting to the right person makes things at least a little better, and any illogical thoughts tend to lose their credibility when spoken out loud and discussed. IMO, venting can be tricky because if you have a friend who doesn't mind listening and helping, it's fine to call that friend and vent. On the other hand IMO, if your friends don't like hearing venting, then it could turn into a boundary violation - you may already know that - but it's a common boundary violation and that's why I'm saying so here. Psychologists are a good place to vent when all else fails.
4. Finding a mentor: This is not necessary or helpful to everyone, but some people overcome test anxiety by a combination of being prepared and finding a mentor who can see their situation from a better vantage point. There's nothing like getting help from someone who understands you and your situation and has been there before. Mentors like this can come in the form of a tutor, a graduate student, an TA/professor/assistant professor, etc. Say a little bit about your situation and see who's receptive.
