When it happens Mild- to moderate-stage dementia
Why it happens It's distressing to realize that "something's wrong" and you're making more mistakes or forgetting things. Between worrying and working hard to compensate for shortcomings, the person is expending a lot of extra mental energy. There can also be an element of denial. Net result: a shorter temper and unwillingness to have mistakes pointed out.
What you can do
Don't take mood swings personally. Even though they seem directed at you, the root cause is what's happening in the brain rather than something you've said or done.
Be as supportive as possible. Don't pick fights, and try to stay even-keeled yourself.
Help the person compensate for memory loss by sticking to routines, leaving notes, repeating yourself, and issuing reminders.
Know that it can help to name the feelings rather than ignoring them: "You seem upset today." "Is it frustrating when you forget things like that?"
Be watchful for signs of depression, which people with dementia are at higher risk of developing.