Insomnia is like a thief in the night, robbing millions - especially those older than 60 - of much-needed restorative sleep.
The causes of insomnia are many, and they increase in number and severity as people age. Yet the problem is often overlooked during routine check-ups, which not only diminishes the quality of an older person's life but may also cause or aggravate physical and emotional disorders, including symptoms of cognitive loss.
Almost everyone experiences episodic insomnia, a night during which the body seems to have forgotten how to sleep a requisite number of hours, if at all.
As distressing as that may seem at the time, it pales in comparison to the effects on people for whom insomnia - difficulty falling asleep or staying asleep or waking much too early - is a nightly affair.
A survey, done in 1995 by researchers at the National Institute on Ageing, polled more than 9,000 people aged 65 and older living in three communities.
Regardless of the reason for insomnia, it can become a learned response when people anticipate having difficulty falling asleep or returning to sleep after middle-of-the-night awakenings. They may spend hours lying awake in bed worrying about being unable to sleep, and the anxiety itself impairs their ability to sleep.
It revealed that 28 per cent had problems falling asleep and 42 per cent reported difficulty with both falling asleep and staying asleep.
The numbers affected are likely to be much larger now that millions spend their pre-sleep hours looking at electronic screens that can disrupt the body's biological rhythms.
Insomnia, Dr Alon Y. Avidan says, "is a symptom, not a diagnosis" that can be a clue to an underlying and often treatable health problem and, when it persists, should be taken seriously. He is director of the sleep clinic at the David Geffen School of Medicine at the University of California, Los Angeles.
So-called transient insomnia that lasts less than a month may result from a temporary problem at work or an acute illness; short-term insomnia lasting one to six months may stem from a personal financial crisis or loss of a loved one.
Several months of insomnia are distressing enough but when insomnia becomes chronic, lasting six months or longer, it can wreak physical, emotional and social havoc.
In addition to excessive daytime sleepiness, which can be dangerous in and of itself, Dr Avidan reports that chronic insomnia "may result in disturbed intellect, impaired cognition, confusion, psycho-motor retardation or increased risk for injury". It is often accompanied by depression, either as a cause or result of persistent insomnia.
A study of nursing home residents showed that untreated insomnia increases the risk of falls and fractures.
There are two types of insomnia.
One, called primary insomnia, results from a problem that occurs only or mainly during sleep, like obstructive sleep apnoea, restless leg syndrome (which afflicts 15 to 20 per cent of older adults), periodic limb movements or a tendency to act out one's dreams physically, which can be an early warning sign of Parkinson's disease.
Unless noted by their bed partners, people with primary sleep disorders may not know why their sleep is disrupted.
An accurate diagnosis often requires a professional sleep study: spending a night or two in a sleep lab hooked up to instruments that record respiration, heart rate, blood pressure, bodily movements and time spent in various stages of sleep.
The other, more common type of insomnia is secondary to an underlying medical or psychiatric problem; the side effect of medications, behavioural factors like ill-timed exposure to caffeine, alcohol or nicotine or daytime naps, or environmental disturbances like jet lag or excessive noise or light - especially the blue light from an electronic device - in the bedroom.
Among the many medical conditions that can cause insomnia are heart failure, gastro-oesophageal reflux, lung disease, arthritis, Alzheimer's disease and incontinence.
Treating the underlying condition, if possible, often relieves the insomnia.
Regardless of the reason for insomnia, it can become a learned response when people anticipate having difficulty falling asleep or returning to sleep after middle-of-the-night awakenings.
They may spend hours lying awake in bed worrying about being unable to sleep, and the anxiety itself impairs their ability to sleep.
The more one frets about a sleep problem, the worse it can get.
Non-medical causes of insomnia are often successfully treated by practising "good sleep hygiene", a concept developed by the late Peter J. Hauri, a sleep specialist at the Mayo Clinic.
That means limiting naps to fewer than 30 minutes a day, preferably early in the afternoon, avoiding stimulants and sedatives, avoiding heavy meals and minimising liquid intake within two to three hours of bedtime, getting moderate exercise daily - preferably in the morning or early afternoon, maximising exposure to bright light during the day and minimising it at night, creating comfortable sleep conditions, and going to bed only when you feel sleepy.
If you still cannot fall asleep within about 20 minutes in bed, experts recommend leaving the bedroom and doing something relaxing, like reading a book (one printed on paper), and returning to bed when you feel sleepy.
Many people resort to alcohol as a sleep aid. While it may help people fall asleep initially, it produces fragmented sleep and interferes with rapid eye movement (REM) sleep, Dr Avidan and others report.
For those who still need help with insomnia, cognitive behavioural therapy has proved most effective in clinical trials.
Sleeping pills can be problematic, especially for older people who are more sensitive to their side effects, including daytime hangover.
Alternatives include over-the- counter remedies like melatonin or valerian, which have more anecdotal evidence than research to attest to their efficacy.
The brain makes melatonin, the body's natural sleepiness hormone, in response to darkness.
There may also be some useful dietary aids, like bananas, cherries, kiwifruits, oatmeal, milk and camomile tea, though evidence for these is also primarily anecdotal.