Both my grandmothers spent about a decade each in nursing homes due to Alzheimers. Both of them had clearly been trying hard to conceal their dementia for several years prior to that, because they were terrified accepting that something was wrong, and terrified of ending in a nursing home.

Once things had gone so far that they could not take care of themselves, and could not manage with the help of their spouses, they just fell apart within months.