I'm really worried about this cough I've been having. After doing cardio exercise, I start coughing really badly and spit out really dark mucus, and sometimes there's even a tiny bit of blood in it. The blood only comes once, but it freaks me out. This happens for about 15 to 20 minutes after my workout, and the coughs feel super deep. The deeper they get, the more black the mucus is, and occasionally, I get this really sharp pain right in the middle of my chest. This has been going on for the last three months. I do smoke around 45 cigarettes a day and have been for the last seven years. I did get a recent medical check-up, and my ECG and chest X-ray came back normal, so I'm not sure what's going on. Can you help me understand what might be causing this?

It sounds like your symptoms could be related to irritation in your airways from smoking, which may cause inflammation and coughing with mucus. While your ECG and X-ray are normal, I strongly recommend seeing a doctor for further evaluation, possibly including lung function tests, to rule out any underlying conditions like bronchitis or early-stage COPD. Cutting back or quitting smoking will be crucial for your health.