Don’t know how to feel

Ladies my nana passed 6years ago and I was always told she passed in her sleep well fast forward I’ve been cleaning my aunts house for her while she’s been in hospital and came across my nana death certificate I read it and it said cause of death cor pulmonale and chronic obstructive pulmonary disease! I was not aware of this so do this mean she was in pain gasping? Like what is that? I’m so upset I can’t stop thinking about it now like could her death been prevented my heads spinning :(

I can’t stop crying like could I of had a few more years with her