Forgetting things can be a frustrating part of daily life.Whether you're left scratching your head after walking into a room – unaware of why you did so – or forget where you put the TV remote, these so-called 'brain farts' can happen to almost anyone.In fact, they're usually caused by a range of factors that affect millions of Britons every day. Experts say stress, mental health problems, a lack of sleep, even hormonal changes and vitamin deficiencies, can all leave you feeling not as sharp as usual.But in some instances, there may be a deeper concern: dementia – the umbrella term for a range of cruel brain-robbing diseases, including Alzheimer's, that almost one million Britons are living with. As well as symptoms such as confusion, changes to a person's language and behaviour, almost all dementia patients experience some form of memory loss.Experts have told the Daily Mail that the most common question they're asked is, 'how do I know if it's a normal memory lapse - or dementia?' 'We know that people are more afraid of dementia than they are of other serious illnesses like cancer,' said June Andrews, a leading dementia expert and professor emeritus at the University of Stirling. Professor June Andrews says 'people are more afraid of dementia than they are of other serious illnesses'Everyone experiences dementia differently. Use this checklist to help you make a note of your symptoms before you talk to your GP.'This is especially true for middle-aged or older people. When they have a problem remembering things, they worry if it is dementia.'The good news, Professor Andrews says, is that most of the time it is not.However, she has highlighted some key differences between normal – albeit irritating – moments of confusion, and potential warning signs of dementia. Forgetting how to do things you previously couldProfessor Andrews says she often hears from people who are concerned they cannot remember phone numbers.But she says that this can be 'normal' if an individual is under a high level of stress or is feeling particularly exhausted.Studies have shown that sleep deprivation can weaken brain cells in areas that are involved in memory. And stress has also been found to affect the brain's memory function, particularly in middle-age.Researchers from Harvard Medical School found in 2018 that having higher levels of cortisol – the body's main stress hormone – may cause the brain to shrink over time and impair memory.Professor Andrews says a more 'serious sign' of dementia, however, would be losing the ability to do tasks previously managed with ease.This can be everyday tasks, like using a phone, or complex activities that an individual is used to mastering as part of their job. Professor Andrews gives the example of a skilled mathematician being suddenly unable to add up. Professor Andrews explained: 'Not being able to remember 10 pages that you had read would be really serious if you were, for example, a barrister or an advocate who was going to be presenting a case in court the next day. 'There's some jobs where it's really important and some where it doesn't matter at all. 'It's a change from what you used to be able to do that matters.'