could be some bacteria being cleaned from your teeth got inhaled with the spray, if you were feeling low/unwell before hand it could possibly be your immune system could not cope with the newly inhaled bacterias. more likely is you cought whatever it is from droplet contact, cold and flu bugs can last for hours floating around in droplet form in the air, it can take a few days for these to show any signs once inhaled as your bodys immune system will try to fight them reducing their reproduction rate but eventually they will be so grate in number that the immune system gets overwhelmed as yours is at present