The 19-year-old attacking midfielder joined on an initial one-month loan deal from Lancashire neighbours Blackburn Rovers in September and scored twice on his debut against Northampton Town.
Accrington Stanley v Yeovil Town
The FA Cup
Second Round Proper
3pm, Saturday 6 December 2014
Store First Stadium, Accrington
Winners receive £27,000 from prize fund
By Wally Downes
And in October his loan deal was extended up until late December and the Republic of Ireland Under-21s star has revealed he settled in straight away.
"The atmosphere is excellent," said O'Sullivan.
"Especially that group behind the goal (at the Clayton End) where the flags are flying. They've been excellent. Every time I get the ball you can hear the excitement, which is a big help.
"As an attacking player that gives you that little extra drive when you get the ball. You want to run at people when the fans are cheering you on.
"You want to make your home stadium a fortress don't you? You want teams dreading coming here after looking at our form. I can't see many teams coming here and beating us to be honest. We just have to keep that going now."
Accrington are currently mid-table in League Two and face the League One strugglers in the Second Round at the weekend.
On home soil they have lost just two matches in the league this season and O'Sullivan says Yeovil will face a tough test when they make the long trip north.
"We want to make sure they are crawling off the pitch with what they have," he added.
"We're fully confident when we play at home with the fans behind us."
