I read your question carefully and I understand your concern. Looking at that description of symptoms I do not think that they are related to Excedrin, those are not typical side effects of excedrin components (aspirin, acetaminophen, caffeine) and the dose of two tablets is not an excessive one. Mucinex maximum strength may cause some sedation and dizziness but it s a rare side effect, so I don t think it that likely, at least not alone. I think your cold as well as the neck problems were the most probable origin of your symptoms. So I wouldn t advise any extra measures apart from rest and hydration which applies to any cold case. I hope you get better soon.