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With 50 percent blockage and that too on one side it is unlikely that you should experience any symptoms at all. But if this is a bilateral blockage then 50 percent will be sufficient to cause symptoms.
Technically, you should be on a blood thinner like a baby aspirin a day and also on lipid lowering drugs like statins or some of the other ones.
I suggest you get a CT Angiography done to assess the severity and pregression of this condition and to rule out any thromboembolic phenomenon such as microemboli that might have caused an infarct somewhere higher up causing your symptoms.
Surgery to remove the plaque at this point in time is not recommended with 50 percent blockage on one side. However, if the disease progresses then an endovascular procedure such as cartoid angioplasty (stenting) can be considered as an option.
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