Sleep, and all the things that come with it, is one of the most mysterious activities we do as humans. The act of simply shutting off our bodies for about eight hours each night while our mind wanders to the strangest of places is bizarre in and of itself. But what about those who suffer from sleep disorders?

They are a lot more common than we think, with almost a third of people experiencing chronic insomnia, and “up to five percent suffering from obstructive sleep apnea,” said Dr. Carl Bazil, director of the Sleep Center at New York-Presbyterian/Columbia University Medical Center. Those with sleep disorders experience a range of symptoms, from an inability to sleep to an inability to stay awake, but most complain they have difficulty concentrating during the days thereafter.

If you think you may be suffering from a sleep disorder, you may not be wrong, but when should you go and seek help? “Discuss it with your primary doctor, if it’s interrupting your relationship or your ability to function throughout the day,” said Dr. Andrew Westwood, assistant professor of Clinical Neurology at Columbia University Medical Center. While some sleeping disorders can disappear on their own, or can be easily fixed by treating the underlying cause, the most telling sign of a sleep disorder is an inability to function.

So what exactly are the most common sleep disorders out there? Click on “View Slideshow” to find out.