Uhh...that's called a troll, for all anyone knows they don't even actually believe anxiety is 'fake' just trying to get a rise out of someone. I mean if you endured abuse it could certainly factor into developing an anxiety disorder...this person on the internet doesn't know you so nothing they say has any bearing on you as a person in reality. By the way you describe it though sounds like they're just being nasty...no amount of explaining is going to convince them the validity of your experience its a common a**hole troll tactic to downplay things someone posts or misrepresent it just to get them all worked up. I understand why you'd be angry at this person its a mean thing to do...but they want you to be mad and dwell on it so best thing to do is think to yourself 'to hell with them' and remember they have no ground to stand on as far as trying to tell you how it is.

Also for future reference if possible its best just not to engage with people on the internet when they start getting personal like that...block em, go to another page for a while, report them if they harrass you. I have dealt with this kind of thing...and more often then not its a trap to get you to engage so they can just upset or even just piss you off by invalidating comments. Admittedly sometimes I still find myself engaging in one of those useless conversations....and gotta remind myself its not worth spending my time and energy...arguing with some jerk or (other unkind words that may not be appropriate here)hiding behind a computer screen. I play an multiplayer online game called League of Legends, and sometimes you get toxic people who insult and belittle people which can really screw up the whole game...but there is an option to report them after the match...so it's not just forums or social networking sites where people behave like that. But yeah it can be hard not to get mad about it, which then of course interferes with trying to concentrate.