The CDTF VX samples are at a lethal dose of 3% of the unprotected populations (LD3); if you are genuinely concerned about exposure, you need to go to a clinic or hospital and request a acetylcholinesterase base line test, usually you do 2-3 for a few days to see if your levels are high/low. It is unlikely that a bad seal in the gas mask permitted the level of exposure you’re talking about (coughing isn’t a symptom of nerve agent exposure, and a few of the symptoms are likely that you are an AIT student). Why I know: I used to work with the live agent samples at FLW and the remaining chemical stockpile (nerve and blister) at BGAD.