First of all, don't beat yourself up about it, we have all been 'there'. Some of us still make the occasional visit 'there' before some trips and tests. A few alternative ideas.
Firstly, take a trip to a major UK high street chemist and get a bottle of Bach Flower Remedy. Follow the instructions and you will be suprised at the results.
Secondly, try and find a local, reputable psycologist/hypnotist (I don't know where you are located). Most will teach self relaxation techiniques. For an investment of maybe £30, you will master a skill that will stand you in good stead for years.
Hope this helps.