I have had that breathing problem - just as you describe it! It is awful and frightening. It's like I forget to breathe. It's better in the day because I'm more conscious of it. It started for me several months ago, but still at a year post-removal. It's interesting to me that you've had the breathing issue while your Mirena is in. I never had it until lately. It must be hormone related.
The first time it appeared for me, it lasted for 3 nights. I literally did not sleep for 3 nights! Then it kind of went away. Since then, it has flared up a handful of times but only lasts a night or two at the most, and not as intensely. But I am afraid of it happening.
I know I've read other posts here from women experiencing the same thing.
I'm so glad you already had the IUD removed! Please keep posting.