If you have acid reflux going into your mouth at night when you are asleep, it is possible the acid is irritating your gums.
Before I was diagnosed with reflux in 2007, I was asymptomatic as far as heartburn, but experienced wheezing and a weird sensation like I had liquid inside my ears or my ears were clogged up. After diagnosis and the start of medication (a PPI), all those symptoms went away within a few weeks.
A physician later confirmed for me that stomach acid can get into and irritate different organs. Apparently, they are all interconnected in some way, i.e., if we don't swallow correctly, liquid can go into our lungs, etc.
There may be other causes for gingivitis like teeth grinding, infection, etc. I don't know if you have confirmed acid reflux or have asked a dentist/periodontist (gum doctor) about your symptoms.
Rose