Why does someone with mild cognitive impairment suddenly do very little and have no energy?

(Chapter 24 My Thoughts and Feelings in my book)

Is this part of having MCI? I think that it could be depression or it could be part of the symptoms of MCI. Perhaps it is too difficult for them to figure out how to do what they once were able to do without hardly much thought. I know sometimes my MCI symptoms can make life exhausting! Sometimes just doing tasks that were once considered simple can now take so much energy because my brain isn’t working the same way as it once was.