If you've ever woken up bewildered by a dream you were having, there's now an explanation as to why.
Scientists have discovered our dreams really do get weirder as the night goes on.
'We found that dreams increase in bizarreness from the early to late night,' said study author Dr Josie Malinowski, of the University of Bedfordshire.
Shortly before a person wakes up, their dreams escalate to a level of the impossible - and never likely to happen in real life - 'like a wild animal tearing up your back garden,' she told TIME.
Not only that, they become more emotional - in both a good and bad way - says Dr Malinowski, a lecturer in cognitive psychology.
During the study, researchers gave 16 people an eyelid and head sensor to monitor their sleep.
They then woke each person up four times in the night, journalist Mandy Oaklander reports.
Participants were asked to recall the subject of their dreams and discuss them - and how they might relate to their life - the following morning.
In the early stages of sleep, dreams tended to be more about the people had encountered that day, such as a TV programme or a book.
Dreams about life events were more likely to feature later in the night.
Dr Malinowski says exploring these dreams can help us get more in touch with our emotional side and behaviour.
She said: 'People feel like they haven't generated them because they're often so bizarre. [But] they're a safe way to explore the self.'
There are two stages of sleep - REM and non-REM sleep. During the latter, we experience slow wave sleep, when our immune system is repaired and strengthened.
However being under the weather can also trigger strange dreams and nightmares, experts say.
Any kind of infection, from severe flu to a kidney infection, can make nightmares more likely, explains Patrick McNamara, associate professor of neurology at Harvard Medical School.
'When we get an infection, with or without a fever, the body needs more slow wave sleep. This is so the immune system can fight the bug.
However, he adds it also has a knock-on effect on REM sleep, delaying the point at which we enter dreaming sleep.
'This, in turn, can lead to nightmares or bizarre, vivid dreams.'
As REM sleep is when we process emotions, this can cause a build-up of unpleasant emotions which may manifest as nightmares.
Some experts also believe premenstrual syndrome can lead to more nightmares.
A 2008 study found women reported significantly more nightmares than men (30 per cent of women's most recent dreams were nightmares compared with 19 per cent of men).
Study author Dr Jennie Parker, a psychologist at the University of the West of England, said the nightmares were linked to temperature changes that occurred at certain times in a woman's cycle.
The increase in the hormone progesterone, which women experience before a period, causes their body temperature to rise and has been linked to PMS-related insomnia.
This can cause night sweats and hot flushes, as well as vivid dreams and nightmares.
'Premenstrual women tend to dream more aggressively and are more likely to remember dreams,' adds Dr Parker.
Not getting enough shut-eye in the week could explain nightmares during your weekend lie-in.
Many women also report more bizarre dreams around the menopause, says Dr Tony Boret, a consultant gynaecologist at Spire Bushey Hospital.
Up to ten years preceding the menopause, levels of female hormone oestrogen significantly drop.
This affects levels of serotonin, a brain chemical associated with hot flushes, mood swings and night sweats, and can lead to sleep disruption in around 15 per cent of women, he says. This can cause excessive tiredness and more broken sleep.
Sometimes our nightmares can reflect waking health concerns, such as breathing problems.
A study published in the journal Dreaming in 2006 found those with breathing problems during wakefulness often reported dreaming about being choked or suffocated; those who perspired excessively while awake often dreamed about sweating.
'Our dreaming brains deal in metaphors and symbols,' says Professor McNamara.
'During REM sleep, the brain tries to capture and process overwhelming sensations, things that are troubling us, or that we can't put into words. It does this through the pictures we see in our dreams.'
- Daily Mail