The 27-year-old's late winner on Friday night launched the nation's Euro 2012 campaign with the victory for which they had hoped.
It was Fahey's first goal since his effort for Birmingham against Reading on the day they were promoted to the Premier League in May last year, and he was at a loss as how to celebrate as his team-mates mobbed him.
He said: "I didn't know what to do. I hadn't scored for about a year and a couple of months since the promotion day, so it was a great way to get it.
"I was a bit shocked, to be honest. It's the thing you dream of when you are a kid - even not so long ago, it was a dream for me to play for Ireland and score the winning goal.
"But the main thing is we got the three points."
Fahey's big moment at the Yerevan Republican Stadium came 14 minutes from the end of a tight encounter and just eight minutes after he had replaced Aiden McGeady.
Robbie Keane and Kevin Doyle caused problems inside the Armenia box and when the ball broke to the substitute 15 yards out, he smashed it right-footed past keeper Roman Berezovsky to snatch the points.
Fahey said: "It was scrappy enough. The ball bounced and they were struggling to get it clear.
"I think one of them knocked out to me and I was just ready to slot it in.
"But the main thing is the three points, everyone realises that. Spain came here and struggled, so it was great to get the three points."
Fahey will now hope for more involvement against Andorra at the Aviva Stadium on Tuesday evening, although he is happy simply to be part of the Ireland set-up.
He said: 'We will see. I am just happy to be involved, so any game-time with Ireland is just brilliant."