But feeling consistently tired can be a sign that something is seriously off with your health. In fact, scientists have discovered that in older adults, this type of excessive sleepiness could be a warning sign for dementia, according to new research. As a result, the researchers concluded that changes in sleep patterns may be an “early marker” or risk factor for dementia in older women. Why is sleepiness linked with dementia? However, Dr. Segil points out that sleep is linked to memory consolidation (where short-term memories become long-term memories) and good health overall.