Can't yawn properly anymore?

Hello!

For about two days (Sunday evening) I've had the problem of not being able to yawn properly or not being able to finish my yawn.
And sometimes, when I'm falling asleep, I feel like I'm having trouble breathing or have brief pauses in my breathing. Eventually, it "goes away," and I sleep normally through the night until morning.

I have no problems breathing during the day or at any other time. My nose is also relatively clear.

I've had this happen a few times in my 18 years of life, but usually only for one evening. I've read about it in other forums and that it's related to stress or something?

Does anyone know anything about this???