Hi, Swelling on the base of the neck and behind the ears can have various causes, including an allergic reaction to the medication. Zocor (simvastatin) is a medication used to lower cholesterol levels, but it can cause allergic reactions in some people. Swelling and hives are among the possible symptoms of an allergic reaction to Zocor. Krill oil is a dietary supplement that contains omega-3 fatty acids and is commonly used to reduce inflammation. While it is generally considered safe, it is possible to have an allergic reaction to krill oil as well. It is important to consult with a healthcare provider if you experience any unusual symptoms, especially if you suspect that they may be related to medication. Your healthcare provider can perform an examination, review your medical history and medication list, and recommend appropriate treatment or further evaluation. If you develop symptoms of a severe allergic reaction, such as difficulty breathing, swelling of the face or throat, or rapid heartbeat, seek emergency medical attention immediately. If you require a personalized response, kindly use the Ask A Doctor service and post a follow-up. Take care. Hope I have answered your question. Regards, Dr. Priyanka, General & Family Physician