Mrs Teo had felt that something was wrong with her for more than a year before she discovered the cause.
She was diagnosed as having mild dementia at the age of 66 in 2013.
She has an interest in current affairs and reads magazines such as The Economist and Forbes. But she found she could no longer follow newspaper reports - by the third paragraph, she had forgotten what the first paragraph was about.
She had always been a "scatterbrain", she confesses, the kind who persistently misplaces her spectacles. But this was more than being absent-minded.
Mrs Teo, who does not wish to use her real name, sometimes loses the thread of conversations within minutes.
Neither could she do simple mental sums. She had to add or subtract the numbers on paper "like a Primary 1 kid".
The important thing is acceptance... Dementia is a new world. You have to learn what to do. I expect the illness to progress. What matters is how long I can maintain my status quo.
MRS TEO, 69, who was diagnosed as having mild dementia three years ago
Although dementia patients are often unable or unwilling to call attention to their condition, her reaction to her diagnosis was unusual - she felt relief.
The 69-year-old housewife says: "I was relieved that at least there is a word I could connect to what I have."
Her husband of 43 years took it harder.
"I was devastated. I thought she was just forgetful. I didn't think it would be that bad," says Mr Teo, also 69. "Until now, I haven't told her what I thought about her diagnosis because I wasn't sure how she would take it herself. But she was very positive."
The couple have two sons in their early 40s, as well as four grandchildren.
Mrs Teo says: "I don't think my sons realise the difficulties I have. I still organise meals and badminton games at our home for their families."
Three years on, however, she remains positive and even hopeful. Faced with an uncharted length of time between her early-stage diagnosis and the ravages of dementia that may eventually come her way, she has a can-do attitude.
"The important thing is acceptance. We're practical people. Dementia is a new world. You have to learn what to do," she says.
"I expect the illness to progress. What matters is how long I can maintain my status quo."
Dementia has a brutal public face.
My memory is not so good and I have lost my independence. I can't learn new things. I have to depend on my husband.
Besides stealing one's memories, the illness, which affects the brain, can alter a person's identity. In some advanced cases, sufferers can no longer speak or recognise their loved ones.
Some also cannot shower or eat without assistance.
After her diagnosis, Mrs Teo took part in a month-long programme at the National Neuroscience Institute that taught her how to manage her illness.
To cope with forgetfulness, she makes lists and uses transparent containers instead of opaque ones because she cannot remember what is in each storage container once she closes it.
"I survive by using a lot of Post-it notes," she adds.
She sticks these notes in places where she cannot miss them - on her desk, the dining table or clipped to her handbag.
They remind her of her daily tasks, such as sending a get-well card to a friend; giving her grandson the new clothes she bought for him; or listing the groceries she needs when she goes to the market.
Meticulous by nature, she would stick notes for her domestic helper on the fridge, for instance, instructing her to cook at least 50g of spaghetti for each family member for dinner.
The couple live by themselves with their helper.
Besides keeping a healthy diet and ensuring she has enough exercise and sleep, she also takes medication called Aricept - these measures help her manage the illness and could slow its progress.
She regularly attends a programme at the Alzheimer's Disease Association, together with her husband.
This comprises activities dealing with cognitive function and fine motor skills, such as doing craftwork, puzzles and games.
Mrs Teo's late mother had a form of the illness called vascular dementia, but family history is only one of a few possible risk factors for dementia, which the elderly are more susceptible to.
When she noticed her symptoms, she talked to her doctor, a general practitioner, about them, but he dismissed her concerns.
Three years ago, she accompanied her husband, a retired company director, to the hospital for a routine check-up following his recovery from prostate cancer a few years earlier.
There, she chanced upon a hospital newsletter advertising a screening test for dementia and signed up for it at the National Neuroscience Institute.
There are days now when she experiences frustration and short- temperedness.
"It's like a double whammy. My memory is not so good and I have lost my independence," she says.
"I can't learn new things. I have to depend on my husband."
About two years ago, they bought a new family car, which had "more electronics", she says. She could not master the more complicated way of starting the new car.
This was compounded by an increasingly problematic sense of direction, another symptom of dementia. So she has given up driving, along with relinquishing to her husband the duties of paying bills and filing bank statements .
Neither does she trust herself to sign cheques. Simple words sometimes elude her and she fears she will write the wrong name or amount on a cheque.
She feels less efficient and, therefore, less confident. "I don't know whether it has to do with dementia or old age," she says. "I've always handled everything in the house, but now, I feel wishy-washy about decisions such as changing the upholstery."
Still, she retains much of her capabilities, so much so that dementia can take a back seat. Because she is in the early stages of the illness, her condition, while not a secret to family and good friends, is not fully acknowledged.
Her younger sister, who is in her 60s, has told her: "You don't have dementia lah."
Mrs Teo says: "I still do a lot of things I like." She enjoys going to classical music concerts and has travelled to exotic locales such as The Galapagos Islands since her diagnosis.
Among the more than 20 files of newspaper articles and other information she keeps on all kinds of topics - "Knowledge is important to me," she says - is a file compiling articles about dementia.
She feels "hope, knowing that the scientific community is working on dementia".
"Someone, somewhere is doing something about it, though a cure will probably not be discovered in my lifetime."
Yet she "never thinks" about what having dementia holds for her in the future- she is too busy to dwell on this unknown.
"My only worry is if my husband passes on. I don't think there's anyone who can look after me as well as he does."
Two sets of breakfast? Something's amiss
When memories leave a person, who else can safekeep them?
For Madam Tan, 64, her diagnosis of early dementia two years ago meant her son has become the custodian of some of her memories.
"I forget and he tells me. I didn't know I had forgotten," she says of his childhood memories of going to Chinatown, for instance.
The retired factory worker, who does not want to be identified, has lived with her younger son, Mr Soon, 39, and his family for about 10 years.
Mr Soon, an executive in the finance industry, employs a domestic helper, but Madam Tan, who is widowed, also helps care for his two sons, aged seven and four.
When his household ended up with two sets of breakfast one day, he realised that Madam Tan had bought a meal, even though she had been told there was one.
Her uncharacteristic forgetfulness prompted him to get her diagnosed.
More people will get dementia in greying Singapore and, some, such as Madam Tan, will probably have to rely on their loved ones to notice that their memory loss is not a sign of old age.
Associate Professor Nagaendran Kandiah, senior consultant at National Neuroscience Institute's Department of Neurology, says: "Memory loss related to normal ageing is isolated, not persistent and often for trivial matters.
"For example, in normal ageing, an elderly person may forget the name of someone they see infrequently. However, an elderly person with dementia will likely forget even the names of people they know well and meet regularly."
In a speech marking World Alzheimer's Day last month, Senior Minister of State for Health Amy Khor said that with one in 10 people aged 60 and older estimated to have dementia, the number of seniors with the disease is set to rise as Singapore's population ages.
While Alzheimer's disease is the most common type of dementia, there are other forms of the illness, such as Frontotemporal Dementia and Lewy Body Dementia. Young-onset dementia can affect people in their 40s and 50s.
A representative for the Alzheimer's Disease Association says warning signs of dementia include changes in personality, as well as difficulties in executing plans, such as following a recipe, or in performing familiar tasks, such as remembering the rules of a favourite game.
Sufferers may also lose track of dates or display poorer judgment by, for example, giving large amounts of money to strangers.
Dr Khor added in her speech that the resources available to people with the disease include the authorities' initiative to expand the capacity of memory clinics by 77 per cent over the past five years so that seniors have access to early diagnosis.
Dr Philip Yap, senior consultant at the Department of Geriatric Medicine at Khoo Teck Puat Hospital, says: "The same factors that help prevent the onset of dementia are equally applicable in delaying the progression of the illness."
These factors include keeping physically active; controlling chronic diseases, such as diabetes and hypertension; and staying socially and mentally engaged.
In Madam Tan's case, she feels her condition has stabilised with regular medication and by keeping herself occupied with yoga, karaoke and a twice-weekly programme at The Care Library, which supports persons experiencing cognitive decline.
Although she does not want acquaintances to know she has dementia - for fear of being "looked down upon" - her inner circle of friends has been supportive.
"They worry about me and will call me at 10pm to check that I've arrived home safely after an outing," she says.