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Did this just come up out of the blue, or have you been dealing with it on a lower level for a while? Your first stop should be your GP - they can rule out any physical causes and then refer you to a therapist. An anxiety disorder won't go away on its own, but with professional help (usually cognitive behavioral therapy) it can be managed really well.
Go see a doctor and bring this up - whether your GP or a psychiatrist directly, they can figure out whether there's an organic cause or if it's more psychological and what kind of therapy would work for you. An anxiety disorder doesn't just pop up out of nowhere, there's usually something behind it, and trying to fix it yourself won't get you anywhere. The sooner you get it checked out professionally, the better - both therapy and medication, if needed, work best when you start early.
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