Memories, hallucinations and delirium

Looking back at your time in ICU, you may have some memories of experiences of things that did not make sense when you were very ill. You may also have a hard time telling what was real or not. Some of these memories and experiences may have been very frightening. You may have felt that your brain and thoughts were not quite working properly.

Some of the things you may have experienced on ICU are:

  • emotional changes, feeling vulnerable, scared, anxious or paranoid
  • unable to think clearly/ clouded foggy brain
  • have trouble paying attention and concentrating
  • hearing or seeing things that are not there (these things at the time would have seemed very real)
  • agitation and restlessness
  • not knowing if it was day or night

You may remember not having a lot of sleep, or feeling sleep deprived while you were in ICU. This can happen even more if you were delirious at night. This is a very common problem for ICU patients and can be very stressful at the time. 

Delirium and hallucinations

The sudden change in mental function, thinking, behaviour and consciousness level is called delirium. Be assured that many people who have gone through severe illness on ICU have memories of experiences like this. These should settle over time.

It is also important to know that delirium is NOT the same as dementia. Also, delirium doesn't lead to dementia.

Many patients on ICU experience delirium. Delirium is a sudden change in mental function. It affects how someone is thinking, their behaviour and their level of consciousness. It also affects memory and concentration.  Sometimes patients with delirium may also experience hallucinations and these can feel very real.

Some patients remember very vivid memories from their ICU stay. Others remember only snapshots and memory flashes. For example they might remember seeing people standing around the bed who could not have been there. Or they might remember things moving in the walls and floors.

Sometimes the hallucinations can be so powerful and elaborate, it may have felt like living in a storyline of a dramatic (and sometimes frightening) movie. These experiences can all be part of the hallucinations that accompany delirium. 

At the time you may have believed these experiences to be absolutely true. Even if everyone around you was trying to let you know they weren't real. Some patients describe this as a feeling they were “there, but not quite there” or like living in an unreal world of dreams. These experiences can be confusing and very scary at the time. Unfortunately, many patients with severe delirium describe these experiences.

What we know about delirium

Despite much work to understand and research delirium, we still have a way to go to fully understand the condition and how to prevent it. We do know that most patients who are sick in the ICU are at risk of delirium.

There is no single cause for delirium. Instead, it tends to happen due to a combination of triggers. These triggers are things like illness, pain, medications and being on a breathing machine. We also know that some people are at greater risk of delirium than others.

Being an older patient with prior cognitive issues or dementia increases the risk of delirium. Those with lots of chronic illnesses before they come to ICU are also at an increased risk of delirium.

This means that a single “one size fits all” cure is not an achievable aim. However, how we assess, manage and treat delirium is something that the ICU staff are very vigilant and diligent in doing.  This will always be part and parcel of the care we deliver to our critically ill patients. We will always be reading research to better understand and treat delirium. We will ensure we are using the best treatments to improve the experience for our patients.

Worrying about what you said during delirium

The nurses and doctors are fully aware of the effects of delirium. They know that some patients may react completely out of character to normal. They do not make judgments on behaviour, no matter how extreme. Do not feel guilty.

Having no memories of ICU

Many patients do not remember their ICU stay. This is common. It can be due to patients requiring strong pain medications. It can also be due to the sedation given to you while on a breathing machine. You may also have been very drowsy for hours to days as a result of being very unwell.

Sometimes, the brain's response to trauma is to block out traumatic memories as a way to protect you. You may be struggling to come to terms with this. It may feel like you have lost a part of yourself that you are desperately trying to piece together.


Some families keep a diary for their loved one of what happened in ICU. This may help you to piece together what happened while you were on ICU.

Where to go for support

General practitioner (GP)

You can talk to your General Practitioner (GP) if you feel worried about how you are feeling.

ICU Follow-up Clinic

Depending on where you are, you might also have access to an ICU Follow-up Clinic. The staff there may be able to help you understand more about your illness and your time in ICU.

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Related topics

This topic was reviewed by an intensive care medicine specialist in July 2022.

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