Or pain

Morphine is a strong painkiller. It's used to treat severe pain, for example after an operation or a serious injury, or pain from cancer or a heart attack.
Morphine: strong painkiller to treat severe pain-https://www.nhs.uk/medicines/morphine/

Please explain the use of "or" and the comma before "pain from cancer..."
I know that "or" is used when you have a choice