I’m not sure what you mean by faking it, but if you’re up at night unable to sleep due to irrational thoughts or have a hard time thinking during the day because constant irrational thoughts are running through you’re brain when nothing in your actual life is leading you think that way, then you’re most likely not “faking it”

The way I’ve been taught to think about it is, if you’re anxious enough to consider the possibility that you could be faking it (which often stems from the anxiety of what others will think of you if you say you have anxiety and it isn’t true) then you absolutely do have it. If you were actually faking it, that thought wouldn’t even have crossed your mind because you wouldn’t care about the consequences of faking it.