I'm experiencing some pain on the left side of my lower rib cage, especially when I breathe. It just came on suddenly while I was sleeping in the evening and I'm a bit worried about what might be causing it. Could you help me understand what's going on?

The sudden onset of left lower rib cage pain when breathing may indicate costochondritis, pneumothorax, pleurisy, or muscle strain; however, it's essential to consult a doctor promptly to rule out any underlying serious conditions, especially if the pain worsens, is severe, or accompanied by difficulty breathing, cough, or fever.