No matter how young or old we are, most of us experience the odd memory lapse. Perhaps it will be forgetting where you put the car keys, or what you went to get from upstairs.
Thankfully, these moments pass. But for those with dementia there is no such relief. Imagine what it's like being unable to recall what you'd done an hour before. Or not remembering how to navigate around your own house or the names of your nearest and dearest. Or knowing what everyday things are for, such as a fridge.
Getting overtired: If the brain is tired, it affects the memory even for those without dementia. Recently, scientists have found out why. During deep sleep, brain waves move memories from the hippocampus - the area of the brain that is involved in short-term memory - to the prefrontal cortex at the front of the brain, where long-term memories are stored.
If this doesn't happen, short-term memories get overwritten with new ones and the consequence is forgetfulness, according to researchers at the University of California, Berkeley.
It is a common misconception that we need less sleep as we get older - in fact we need just as much, the problem is that older people find it harder to reach a deeper sleep.