The 59-year-old was thrilled on Wednesday evening when his side secured a second victory in his three games at the helm to date with a 3-2 win at QPR.
However, he acknowledges that his mood can change markedly when things are not going so well.
"I'm always ebullient when we are winning games. Wait until you see the other side," he said.
"It's pretty dreadful, honestly. It spoils my day and then what happens is I go and spoil other people's day, like my family.
"But Wednesday night was just fantastic, really fantastic. Just winning a football match is great. It doesn't leave you."
Six points from a possible nine have left smiles on the faces of O'Neill, his players and the club's supporters and eased the Black Cats three points clear of the Barclays Premier League drop zone.
However, the Ulsterman - whose men face Everton and then leaders Manchester City at the Stadium of Light over the holiday period - insists that while his first few weeks on Wearside have been hugely encouraging, they represent just a start.
He said: "It's encouraging. We badly needed some points on the board and that's been achieved. But we have still a long way to go, obviously."
O'Neill has endured a whirlwind start to his tenure and the intensity is only likely to increase with the games coming thick and fast and the winter transfer window approaching.
However, he insists he is enjoying it, particularly when things turn out as well as they did at Loftus Road.
"In a sort of perverse way, I am," he added. "Naturally the winning of football games, the feeling in the dressing room, the players were elated and the feeling was shared by everyone.
"Just winning football matches, it's really fantastic. I am still euphoric. I will come back down to earth, but allow me a day or two to enjoy it.
"The victories are great. You celebrate them, seemingly, for about 10 minutes, and defeat seems to last about a week, so I am going to try to reverse that."
Speculation is already mounting over what O'Neill may be able to do in the transfer market next month, although the prospect of Asamoah Gyan returning from his loan spell at United Arab Emirates side Al-Ain has receded.
The agreement which took the Ghana international to the Middle East covers the entire season, and in any case he will be on African Cup of Nations duty within the next few weeks.
Sunderland have already been linked with a series of potential targets, many of them understandably strikers in the wake of the departures of Darren Bent, Danny Welbeck and Gyan.
The name of Fulham's Bobby Zamora was added to the list on Friday, although O'Neill was coy when asked about the suggestion.
He joked: "We have been linked today and we are going to be linked, in the not-too-distant future as January progresses, with players.
"We are linked with some really good players, we have been linked with some pretty average players and we have also been linked over the course of time with some pretty abominable players.
"I just want us to be linked with the really good players."
However, there could be some good news on the striker front just around the corner with Fraizer Campbell rapidly approaching contention after his latest knee injury.
O'Neill said: "He is doing very well. He played this morning again for about 75 minutes and the medical team have said to me that there's not much more they can do.
"They are sending him out, he doesn't seem to be having any reactionary problems to anything, so that's very encouraging."