Seeing things that are not there is common in delirium. To the person, what they see feels completely real.
Delirium affects how the brain makes sense of what comes in through the eyes and ears. Real things get built into a wrong picture. A dressing gown on a door becomes a person watching. A drip line becomes something holding them down.
Some people also believe things that are not true. For example, that staff mean them harm, or that they have to leave for work. These are symptoms, in the same way a rash or a fever is a symptom.
What helps
Arguing does not help. You cannot reason someone out of a hallucination, because to them it is really there.
Respond to how they are feeling rather than trying to correct what they are saying. You can say something like: “I believe this feels real. You are safe. I am here.” Then offer something ordinary and true: who you are, where they are, that the doctors are looking after them. If they say something odd but are not distressed, you do not need to correct it at all.
Tell the staff
Tell the staff what the person is seeing, especially if it frightens them. Distress can be treated, and its causes can be looked for.
If the hallucinations have just started
If someone was thinking clearly yesterday and is seeing things today, that is new confusion. Get medical help the same day, and ask: could it be delirium?
As the delirium clears
Hallucinations usually fade as the delirium clears. Many people remember little about them. Some remember them clearly and need to talk about it. There is more about whether they will remember it.
When to get help
New confusion that has come on over hours or days needs medical advice the same day. Phone the GP practice, or 111 when it is closed. Phone 999 if the person cannot be woken, has collapsed, or has new weakness or new trouble speaking. When you speak to someone, say what has changed. Then ask: could it be delirium?