The Tottenham central defender was axed from the provisional squad of 30 for the South Africa tournament on Tuesday by England coach Fabio Capello.
But Dawson has been summoned to join the 23-strong party after Ferdinand was forced out with a knee ligament injury suffered in training yesterday lunchtime.
Dawson told Tottenham's official website: "It's a crazy game and things can change in a split second. One minute I'm trying to arrange my holiday, then I get a call asking if I was on holiday because Rio had pulled out of training.
"I said 'no' and then I was just waiting by the phone before getting a call saying I would be picked up in an hour. It's been a crazy day."
Dawson has immense sympathy for Ferdinand but is determined to try to seize his opportunity, saying: "For Rio to get injured, there would be no worse feeling for him as a player.
"To miss the biggest tournament in the world as the captain, I feel for him. I missed the League Cup Final in 2008, and there was nothing anyone could have said to me that could have made me feel any better. For Rio, the feeling will be the same, but it's a chance for me now."
Dawson, who was Tottenham's player of the year, added: "I've not had time to think about it but I've had call after call with people wishing me good luck.
"I know all the lads through having been with them for two weeks so I'll just be going out there and training as normal. I was planning to watch the first game of the tournament with my friends and family, but now I'm going to be there for real.
"I'll be going out there still having not yet won a senior cap, so where better place to get one if that was to happen?
"But I'll just go there and train like I do every day at Spurs and we'll have to see what happens."