Having seen most (but not all) of DS9, Garak had his fair share of mental issues and anxieties.

He was just also really good at masking.

struggle with the social anxiety of answering a phone call.

I'll have you know I work on my conversation and interpersonal assertiveness skills by talking to the telemarketers.

his father-mentor was the head of the Cardassian CIA

I think that does him a disservice. you know about the CIA. The obsidian order was a myth that nobody wanted to validate as real.