What is the word for when you feel like a fake? You are not trying to cheat anybody, but know that you are simply out of your depth / out of your class about something. This especially happens in technical conferences. There is a word for it but I don't remember what it is.
Sounds like you’re talking about the recently described phenomenon that has come to be called impostor syndrome, which Wikipedia says is:
a term coined in 1978 by clinical psychologists Dr. Pauline R. Clance and Suzanne A. Imes referring to high-achieving individuals marked by an inability to internalize their accomplishments and a persistent fear of being exposed as a "fraud".
Around a year ago now on October 26, 2015, Carl Richards wrote a New York Times piece entitled “Learning to Deal With the Impostor Syndrome” discussing “this fear that you’re bumping up against the limits of your ability”.
Apparently this is a common sentiment amongst high-functioning individuals. Given the nature of technical conferences, it is easy to imagine someone attending these feeling so overwhelmed by the dense technical topics they’re being exposed to there that some would find themselves stricken with impostor syndrome.
You might also like to say that you went through or are going through
a crisis in confidence
Attempting to impress by affecting greater importance (talent, culture, style, intellect, knowledge, skill etc.) or merit than is actually possessed.
‘He also had a convoluted and elaborate manner of speech that many thought pretentious.’
‘pretentious art films’
‘the pretentious jargon of wine experts’
Mid 19th cent ury: from French prétentieux, from prétention (see pretension).
lacking the quality or quantity required; insufficient for a purpose.
"these labels prove to be wholly inadequate"
synonyms: insufficient, not enough, deficient, poor, scant, scanty. — Oxford Living Dictionaries