Ms Bailey said it was an extraordinary privilege to address the conference given Australia was not a NATO member and she wished a photo had been taken of that.

"For the photographer to take a photo like that I think is pretty low," she said.

"We really worked our butts off in Brussels to set up these meetings."

Representing Australia, Liberal MP Fran Bailey grabbed a spot of shuteye during her taxpayer-funded appearance at the NATO Parliamentary Assembly in Edinburgh, Scotland.

It’s not the first time Ms Bailey has fallen asleep on the job.

Last year in Parliament, Labor MP Anthony Albanese asked: “I wonder if someone can get the Member for McEwen a pillow.”

“She is constantly asleep!” Labor MP Daryl Melham interjected.

Meanwhile, a sleep expert said Ms Bailey may have a medical condition, but her colleagues suggested she may not have been sleeping at all.

Despite Ms Bailey being slumped in her chair, fellow MP Sharman Stone said yesterday she might just have been taking an extended blink, the Herald Sun reports.

"Whoever took the photo might have grabbed her at a second when you shut your eyes," she said.

But professor of sleep medicine for the National Health and Medical Research Council Ron Grunstein said it was no laughing matter and that she might have a serious problem.

"My big concern is that the public and also the media must understand that repeatedly falling asleep in inappropriate situations is often a sign of a medical condition," he said.

"Conditions that make people sleepy like sleep apnoea are no laughing matter. They are treatable medical disorders."