The mechanism by which it lowers your BP is by reducing your heart rate (beta-blocker). Be careful with 100 mg doses after not taking any beta blockers for awhile as you will have no or little tolerance. You don't wanna drop your BP or your HR too much, or have bradycardia. Generally beta-blockers are the opposite of recreational. They can actually cause depression and lack of energy. The only thing it will do for you, as stated earlier, is help with the physical symptoms of anxiety (heart rate increase), and possibly some very minor CNS effects. Relieving the physical symptoms of anxiety can help quite a bit for some people. This is a drug used for stage fright as well.
edit: Do not take more than 100 mg in a single dose definitely, but 50 is probably a better recommendation, like the doctor prescribed. You can have fatal overdose from beta blockers. The more you take past the therapeutic dose, the worse of a time you are going to have.