Paranoia, guilt, yearnings, accusations, mistrust, stubbornness, disbelief, confabulation, and very occasionally, unintentional (due to diminished responsibility) killing.
Dementia causes a persons brain to disconnect. What was acceptable becomes unknown. Behaviour becomes unpredictable. The difference between what is, and what is not acceptable, becomes blurred.
My Uncle, who had Alzheimer's, had no issue, when in a nursing home, with dropping his trousers and exposing himself to everyone around. Apparently, something he used to do, as a child. Some can become very obsessed, sexually.
When it comes to money, my Mum, trusts no-one. She wants to know exactly what has happened to her money, and how it's been spent. She was always meticulous with her bank accounts, and is almost manically obsessed with money.
These are just some of the extremes, yet dementia presents other, more mundane problems.
Eating and drinking
There are times, no matter how hard you try, Mum or Dad will tell you that eating and drinking is not essential. For a care giver, this can be almost unbearable. You know they need to eat and drink, yet they refuse, and tell you, "you are talking rubbish".
As a carer for a loved one, this is incredibly difficult to handle. The more you tell them they need to eat or drink, the more stubborn they can become. Patience, and gentle persuasion, is the order of the day. Yet, it is so difficult to maintain. You care. You know they need to eat and drink. You become angry and frustrated. Their response is to become more stubborn still. Walk away. Stay calm. Reason.
Go back, discuss, and gently, not forcibly, try to get them to understand. Sometimes, it is better to leave it for half an hour, or more. They may have calmed, may have forgotten, and may have become more receptive. Try again - calmly. Don't force or provoke. If they appear receptive, build on it. If they're still belligerent, leave it. You may not think it's right, but they have a choice, to which they're entitled. Forcing them to do something is abuse, and needs to be avoided at all costs.
If you're a main carer, you will undoubtedly bear the full barrage of insults and accusations. Whatever the problem, it will be your fault. They'll still love you, but will also hold you responsible for anything that has gone wrong. Accept it. Don't fight it.
Yearning for the past, is common. They want to go back to a time when they remember love, happiness and security. Don't resist. Play along. This can be difficult at first. Just remember the memories of the times when you were a child. That, is what they're yearning for.
DANGER - there have been a few (very few) isolated incidents, when dementia has led to a killing. This has often been due to paranoia, mistrust and irrational jealousy. Whilst these conditions and emotions are not uncommon, it is essential that they are understood. Especially when a spouse, is caring for a spouse.
Most people living with dementia, can continue to lead a perfectly normal life. Awareness of the darker side, can help those living with dementia, and especially those caring for them.