One technique that sometimes works – and it can be fun to do regardless of whether it “works” or not – is to imagine “What’s the worst that could happen?”
Be outlandish in this exercise of imagination:
– I could be hit by a meteor while taking a test on astronomy. (Well, that could happen during math class, too, or even English lit.)
– If I study biology, I could accidentally invent and then contract some hideous and slowly lethal disease.
– If I study oceanography I could be eaten by a shark.
– I might be so nervous while taking a test that I wet my pants.
… and so on.
Maybe some of those are, in fact, too close to the mark, and instead of making you smile or laugh you start to think, “That could really happen! I do get nervous enough that I could wet my pants!” Speaking as one who was too scared to raise a hand in class and ask for permission to go to the bathroom in fourth grade and did wet his pants – in fourth grade! – I sympathize completely.
But those are the ones to attack even more relentlessly. Make even more and more creative imaginations of “what could happen if…” And if you come across one that you simply can’t – in the end – smile your way past, such as if you really are afraid of incontinence due to nervousness, then you need to develop a coping strategy to deal with this real problem: adult diapers, for example, or “no drinking before test days” (you’ll live, even if you have to go a full day without drinking; it will be uncomfortable, but you’ll manage just fine – and have a win at the end of the day).
But just making the list – and the more outlandish and creative, the better – can be relaxing and fun in itself. You could make it a social thing, where you invite others to participate. And you might eventually realize that most fears, most of the time, are just as groundless as the fear of being eaten by sharks or hit by meteors. Yeah, those things actually happen, and it’s pretty awful when they do, I guess, but that’s not often, and not worth worrying about.
Maybe this advice is contra-indicated for someone with actual anxiety issues; I wouldn’t know about that. So if you try something along these lines and it actually makes your anxieties worse, then talk to a professional about it. But this can actually work for a lot of people.