My mother, who has Stage 4 non-small-cell lung cancer, was coughing up blood recently. The doctors thought it was just the progression of the disease. She ended up in the ER due to low oxygen levels and shortness of breath. She was admitted to the hospital thankfully because that night she went unconscious and they called a Code Blue and had to resuscitate her and intubate her.
The ER doc who intubated her thought she may have had a blood clot in the lung. There is a test you can do to find out but they didn't do it because the remedy for a blood clot is blood thinners. When you're coughing up blood, they won't give you blood thinners.
Thank the Lord, she had great doctors and was in the hospital when she went unconscious. She is now at home, on oxygen, and getting radiation treatments to her lungs, every day, M-F, for four weeks.