So, my girlfriend (22) has diagnosed panic disorder. She has panic attacks maybe once or twice a month. Sometimes they are triggered by things that happen around her, sometimes they have no apparent trigger. 

However, for many years she's had these... let's call them "hyperventilation episodes" during the night. She'll start hyperventilating during her sleep, and she'll keep going for several minutes until she eventually stops and continues sleeping as if nothing happened. She does not wake up during these episodes and she only knows about them because people have told her. If I wake her up during an episode she proceeds to breathe normally and she doesn't remember dreaming anything or experiencing any panic/fear. 

I recently started wondering whether these episodes are related to her panic disorder because hyperventilation is also one of the symptoms she experiences during a panic attack while awake. I tried googling the symptoms and found a lot of articles on "nocturnal panic attacks". However, one of the main points of these seem to be that you wake up in the middle of a panic attack. But, as I said, my girlfriend does not wake up during these episodes. And I wasn't really able to find any other explanation that made sense. 

So, has anyone else had similar experiences? Or do you have any idea what could be causing this? Or is it not related to anxiety at all? 

Thank you all