One-sided weakness can be a sign of stroke. Here are other common symptoms:
Sudden vision changes
Sudden problems walking
Sudden, severe headache
Sudden inability to speak
Most of the time, the symptoms of stroke come on suddenly, but this is not always the case. If your one-sided weakness has developed gradually and seems to be getting worse, you should see a doctor.
I can't think of any reason why anxiety would cause one-sided weakness. I suppose it's possible it could be a medication side-effect, but this still deserves to be checked out. I suggest you call your doctor as soon as possible.
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