It's a phenomenon reported by many.
But there is little evidence the 'midlife crisis' exists, according to a psychologist.
Professor Nick Haslam, of the University of Melbourne, claims midlife is a time of growth that 'requires a process of adjustment'.
And he said 'unsurprising' studies have shown older adults choose midlife as the phase they most prefer.
'It's hard enough deciding when the midlife crisis should occur,' he said. 'Concepts of middle age are elastic and change as we get older.'
Various studies that used surveys state middle age to be anything between the 30s to 70s, Professor Haslam said.
However we define midlife, studies suggest that self-reported crises 'simply become more common as we age', Professor Haslam said.
Evidence also points towards life generally becoming more positive around this time, as the personality becomes more stable.
He pointed to a Swiss study, published in Gerontology in 2009, which showed that the older the participants, the older they reported their midlife crisis to have occurred.
Psychoanalyst Elliot Jaques, who coined the term 'midlife crisis' in 1965, thought it reflected the dawning recognition of death.
But others suggest it could be related to children flying the nest, having to care for ageing parents, chronic illnesses beginning to show and work demands.
However, it could be biologically rooted, considering chimps and orangutans have shown signs of a dip in mood around a similar age.
The study, published in PNAS in 2012, by international researchers, found monkeys found the least pleasure in social activities at this age.
Although it is speculated that events can trigger crises, there is no clear connection, Professor Haslam said.
'Crisis episodes may not be tightly tied to adverse life event,' he said. 'Research often fails to show clear connections between adversities and self-proclaimed crises.
'One study found reporting a midlife crisis was not associated with recently experiencing divorce, job loss or death of a loved one.'
Generally, people go through a positive transition in what they perceive to be their midlife, Professor Haslam said.
'In general, psychological changes during midlife are positive. Personality becomes more steady and self-accepting, while positive emotion, on average, gradually rises through the lifespan.
'The U-shaped life satisfaction curve notwithstanding, most change during midlife is positive.'
Professor Haslam said one longitudinal study, published in the journal Assessment in 2000, found American women from the age 41 to 50 became more resilient as they aged, as they became less neurotic and self-conscious.
'Middle age may be dislocating for some but there is little evidence it is usually a period of crisis and despondency,' Professor Haslam said.
'If there is a small dip in how people evaluate their lot – even if it is objectively no worse than before – this is understandable.
'Psychologically speaking, things tend to get better.'