This is a new one to me, but I find it completely plausible. According to the Melbourne Sun Herald,

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

Sleep specialist Dr David Cunnington, of Melbourne Sleep Disorder Centre, 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.”…

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

“Emails 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.

Dr 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 emails constantly, and get notifications from smartphones, it becomes more difficult for us to separate our waking and sleeping lives.”

Part of what’s interesting about this is that sending a text isn’t that easy: one person 

sent two multimedia text messages, apparently after falling asleep during an exchange with her boyfriend.

The first began “Baby u there? Need to tell somethin …” before it turned into nonsense.

To do so, she had to navigate 11 different stages, excluding the typing.

As the Kansas State Collegian wrote,

According to a study done by Pew Research Center’s Internet and American Life Project, young adults send approximately 3,200 text messages each month. Now, a growing number of people are starting to send texts in their sleep.

People have reported that they send text messages in the middle of the night and have no memory of it in the morning. Sometimes, sleep texts are logical messages, but they can also make little sense.

“My roommate wakes up to texts in the middle of the night, starts to answer with gibberish and then falls back asleep,” said Jessica McAllister, junior in elementary education…. “It just shows that our daily addictions become ingrained in our subconscious to the point where we automatically do this without even knowing,” said Richard Kim, senior in architectural engineering….

Cunnington and other researchers suggest that those who are suffering from sleep texting should leave their phone outside of the bedroom for a better night’s sleep.

No kidding.