60 year's old male patient of moderately severe chronic obstructive pulmonary disease

Question

The patient has quit smoking last 5 years and developed sore throat and fever. Tablet paracetamol 500mg 3 times a day till fever persists. After 3 days he presented with pain in epigastrium, restlessness, irritability, inability to sleep, palpitation. Tremor of finger and hand and had vomited twice. His fever had vomited twice. His fever had subsided and throat was better. Then what could be the reason for his recent illness?