There are many reasons for brain congestion after a cold with a hangnail, such as disease factors, too fast infusion, adverse drug reactions, etc. 1. Disease factors: During a cold, viruses or germs will increase in large quantities, and when endotoxin is released, it acts on the nerves, thus causing discomfort in the head. 2. Too fast infusion: too fast infusion will lead to rapid increase in blood pressure. In addition, if the patient is fasting, the metabolic level of the body is weak, when subjected to external stimuli, adrenaline is released into the bloodstream, resulting in rapid heartbeat, elevated blood pressure, nausea, dizziness, head stuffiness and other adverse symptoms. 3. Adverse drug reactions: antibiotics or antipyretic and analgesic injections may be used during the treatment of colds and flu, which may induce dizziness, nausea, head stuffiness and other symptoms if one is more sensitive to the drugs. After the medication is stopped, this symptom will gradually subside. If you feel unwell after a cold or flu, you should consult your doctor in time to avoid adverse effects on your health due to delay.