Senile dementia, also known as Alzheimer's disease, is a degenerative disease of the central nervous system. As the disease progresses, patients experience a decline in their memory, comprehension, language expression abilities, and mobility.

As for whether patients with dementia feel pain, it largely depends on their own state. During the early stages of the disease, when patients are often still awake and aware of their surroundings, they may experience feelings of self-blame and other emotions, such as pain and excitement. This is often because they do not want to be a burden on their families.

In the later stages of the disease, when patients have more severe cognitive dysfunction, they may not have a clear understanding of their own behavior and may not experience as much pain.

Generally speaking, if Alzheimer's does not significantly affect a patient's daily life and they can still eat and take care of themselves, they may experience little pain and may not even realize when distressing things happen. However, if the disease does affect their ability to function normally, they may experience pain and discomfort, as well as increased emotional sensitivity.