I have had this fear on And off since oct 2012. Reassurance seeking doesn't help, and I have experiences the migration of this fear to others as well. Just accept the worst possible scenario and deal with these possibilities. You can search the forum and I went into quite a bit of detail with this specific fear, might help you short term . But long term, Dealing with this fear is difficult because of water exposure everywhere. The thoughts always come back to me no matter what. I still sometimes take a flashlight to check up my nostrils to see if any there is any water in certain situations. Thank the media and fear mongering for this one.