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.
There are things we can do to reduce the risk of dementia.
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.
Getting a good night's sleep can be especially difficult for those with dementia, especially those with Alzheimer's disease who may experience changes to their sleeping patterns. Quite why this happens is not understood, but it may be related to the impact the condition has on the brain. But there are steps that can make it easier. One of the most important measures is to avoid catnapping during the day (this becomes harder to avoid as dementia becomes more advanced). Catnapping makes it both harder to fall asleep at night and more likely you'll wake up earlier than desired.
Limit use of stimulants: Other steps include avoiding caffeine - coffee or tea - in the evening. A regular bedtime is also important as this gives the body the cues it needs to feel sleepy at set times, making it easier to fall asleep.
Although many people believe a nightcap will help them sleep, alcohol is also counter-productive and tends to make you wake in the night. It is a diuretic and, therefore, you are likely to wake up needing to go to the loo. It is also known to reduce the amount of the night you spend in deep, restorative sleep.
Eating too much junk food: Cakes, chips and biscuits won't just impact on the waistline - they can adversely affect your memory, too. Recent research has found that regularly eating food high in fat and sugar leads to inflammation in the hippocampus. Scientists at the University of New South Wales, Australia, found that eating these foods every day caused inflammation in the brain after just one week.
Smoking: Many studies have found that even occasional smoking can impact on the brain. One study, from King's College London, analysed 8,000 over-50s and found that smokers performed worst in memory tests, learning ability and reasoning.
Not 'using it': When someone is diagnosed with dementia, they often start to withdraw from their normal hobbies and activities. Yet to retain your mental ability and memory skills for as long as possible you need to keep the brain stimulated.
Just as our bodies need physical exercise in order to stay as strong as possible so, too, do our brains. It's a tried-and-tested principle: for example, a review of 15 studies by the respected Cochrane Library looked at the benefits of a variety of activities designed to stimulate the brain and promote memory such as word games, puzzles, listening to music and practical activities such as baking and indoor gardening.
