When I went through this with my grandmother, I experienced that too. Like others said, it's important to note that in the later stages it may be hard for the patients to communicate their pain, so we cannot be sure, but at least in my anecdotal experience I would say that I can be pretty sure there was no acute pain involved.

The most important thing for me and others around her was to just vibe with her reality. Just give her the space. Not be mad, but laugh or help, again and again. Like you would do with a baby. Don't expect them to learn, don't expect anything.

Until the very end I think she had a good life. The end, obviously, will have been hard for her, because that's a time where they cannot even live their own little life anymore but probably experience higher pain in general, but that's what it is.