I have had it a couple of times. It is because I have silent aspiration, or that some of what it drink ends up in my lungs. Usually not a big deal ( though it is getting worse as the years out from treatment accumulate) unless I am down ill for a week or so. Then my lungs do not clear since I am on my back too much, and bang -into the hospital with full blown pneumonia. Some silent aspiration is common after treatments, depending on where the tumor and radiation targeting were.