The breathing part sounds like you could have
sleep apnea.
In sleep apnea, your breathing stops, or becomes very weak, while you are sleeping until your brain wakes you up and you take a breath. This kind of sounds like what is happening in the dreams. I think you should definitely have this checked out.
The first dream, about being in a medical place, also seems to be a message that there is something medically wrong.
Death in a dream can also represent change, so the dream about being afraid your breath slipping away could have to do with a fear of change - the rollercoaster could have to do with taking risks.
But I think you should definitely have yourself checked for sleep apnea first.