Just started Smartvest therapy last night

I just got a smartvest. I don’t have guidelines yet for when to use it, but did for 15 minutes last night and 20 for today. I feel like it’s working- I’ve been coughing quite a bit more than usual and feel like I’m bringing up more than usual. I generally can’t cough up much at all, to the point where I can’t get enough for a good sample. This morning since I’ve used the smartvest I’m feeling quite short of breath. I’m thinking it’s from loosening up phlegm which needs to be coughed up and just isn’t “up enough” for me to clear. Just thought I’d get some opinions from others and ask if anyone else experienced this in the beginning of their vest journey?