hyper is very right,your sinuses are encased in bone and tissue,there is no way you would have had that stuff suddenly 'hit' your brain,so please don't worry over this.you probably just hit too much(more than you are used to?) mucosal tissue at once and it absorbed thru that tissue pretty rapidly.i am pretty sure you are okay,K?FB
just an FYI,i ALWAYS tip my head back when using a nasal spray,was never told to actually DO anything else differently.