Is a cancer death painfull? how would it happen would you just fall asleep?

Depends: It depends upon the type of cancer and the care that is being given. Many time before someone dies they slip into unconsciousness and then just stop breathing. Some forms of cancer are more painful than others. It is always helpful to have palliative care or hospice involved to make sure the pain (if present ) is treated adequately and the patient is made as comfortable as possible.

Varies: My other colleague answered your question well so I will not repeat it. I'm concerned about you, though. I see a lot of questions regarding cancer coming from you. Anybody in your family with this? If so, I am very sorry but if this is just being worried about things, please don't. At your age this would be exceedingly rare and I hate to see someone not enjoy the gift of life because of worries.