This condition results in decreased mental functions in the areas of memory, awareness, and acuity. It can be severe—significantly interfering with daily activities—or mild. While it's most often associated with aging and mental conditions like Parkinson's, dementia, and Alzheimer's, other factors can contribute to it, such as depression, illness, sleep deprivation, medication side effects, nutrition deficiencies, a traumatic brain injury, and diet and health choices. 

The eyebrows pulling together
Biting the inside of the cheek
Fidgety movements
Glancing around in confusion
Struggling to find the right words
Easily becoming flustered 
Using the wrong words when speaking
Difficulty following the conversation when several people are involved 
Showing frustration when communication is difficult
Short- or long-term memory loss
Making errors during familiar tasks, such as managing household finances
Losing keys, a wallet, phone, and other items
Putting familiar items in unusual places
Forgetting about appointments 
Difficulty with complex tasks that used to be relatively easy
Getting lost in a familiar place
Being unable to get to a place they've been to dozens of times
Snapping at people
Being irritated by small inconveniences
Telling the same stories and asking the same questions 
Needing clarification more often than is normal