The stress of daily life has sparked a new phenomenon -- sleep texting.

People with the rare condition send incoherent text messages while asleep to their friends and family, and are completely unaware they are doing it.

Sleep specialist Dr. David Cunnington, of the Melbourne Sleep Disorder Center, said patients had reported sleep texting.

"We have had patients who have reported sending text messages to their friends and family while asleep," he said. "It is one of those things that happens, but it is very rare, and certainly not a common trend."

There are no studies into sleep texting, but a similar phenomenon, sleep emailing, was studied in 2008.

Researchers at the University of Toledo in Ohio reported the case of a woman, 44, who would compose e-mails while sound asleep. She had no recollection of sending the e-mails when awake.

Cunnington said cases of sleep e-mailing were more common and were likely to have a more detrimental effect on the lives of sufferers.

"E-mails can be sent to work colleagues and have much more serious consequences, whereas text messages are more likely to be accidentally sent to a friend or family member, so people aren't as likely to complain of a problem," he said.

Cunnington described sleep texting as the result of people having too much to do during waking life.

"People are doing so much during a normal day that it can mean that they feel like they're 'on call' even at night," he said. "Because it's so easy to receive e-mails constantly, and get notifications from smartphones, it becomes more difficult for us to separate our waking and sleeping lives."

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