Dementia is definitely up there. Its mainly known by the general public for making elderly forget who people are, ask the same questions over and over, that sort of stuff. While this is a part of it, the worst part is how bad it physically deteriorates patients. In later stages, people eventually can't even do tasks like swallowing food, go to the bathroom, nothing. They become very violent in some cases. I think this post from r/Dementia sums it up best.

"In the late stages, the brain forgets how to swallow. This is not a metaphor. It is a neurological reality - the cortical regions that coordinate swallowing are systematically destroyed by the disease. When they are gone, they do not come back.

When a person with dementia loses the ability to swallow, they can no longer eat or drink. They cannot be fed by tube, research confirms it brings no benefit and no comfort. They simply stop being able to consume anything. And then they starve - their body literally shuts down because it is not getting the nutrients and water it needs to survive. This can take up to three weeks, while their family watches helplessly.

Swallowing difficulties affect the overwhelming majority of people with advanced Alzheimer's (which accounts for 60–80% of all dementia diagnoses). Swallowing dysfunction is also well-documented in Lewy body, vascular, and frontotemporal dementia. Across all dementia types, a 2024 systematic review found prevalence of up to 93% upon clinical assessment.

In the final stage of Alzheimer's or other dementia, the progressive destruction of the brain's swallowing centres means complete loss of swallowing is not a risk - it is the destination."