I'm wondering if your breathing issue is really what is commonly called the "MS hug"? There are muscles that go around your torso (and around your arms, head, and legs). If they get affected by spasticity...and sometimes it can be a matter of a sensory issue and not spasticity...
it'll feel like you are being "squeezed in" -- thus the "MS hug". I liken it to your lovely elderly Aunt Sadie who comes to visit and insists on giving you a BIG hug, smothering you in her...uh...chest.
Folks have been known to rush to the emergency room thinking they're having a heart attack, or collapsed lung or something..to find that everything checks out "negative"...no heart attack, the lungs are functioning just fine, the diaphram is doing what it's supposed to do ... just the sensation of being squeezed, and that you're "not getting enough air".
With all the other spasticity occurring right now for you, I'd bet that it is the spasticity of those muscles. Sometimes this is called "banding".
Do call your doctor and at least report this occurrence. Even if he doesn't want to treat it (or you don't want to do steroids) it should be noted in your records that you're experiencing an exacerbation. I hope you feel better soon.
You can take more baclofen than you're currently taking too -- but again, don't increase (or for that matter, decrease!) the dose of baclofen or any other med without talking with your doctor!
...I am not a doctor, nor health professional, and don't pretend to be one, here.....