Never having won the lottery or any other prize like that, I can only comment on other people's experiences. Many of those who went public are sorry that they did, because they received sacks and sacks of begging letters from all over the place. They got people stopping them in the street and asking for money, they couldn't go anywhere without being recognised!
I know those people have said, "It was difficult to keep it a secret." And sometimes you, or your partner might be the kind of person who just cannot keep a secret. I remember reading a book a long time ago about a woman who won the football pools (it was before lotteries). She won £1million, which was a lot of money then. She knew her husband would not be happy without his work to go to, so she used the money to help save the firm he worked for, without telling him anything about the win. That kept him happy and she enjoyed the money that way, because he got promotion and bought her small presents and flowers which she appreciated much more than large sums of money.
I remember reading a tip from someone some years ago about the Irish lottery. That person said that if you couldn't keep a secret, wait until the lottery was won by several people so it seemed like you only won a "small" amount, or say that you had one one of the lesser prizes. You're not as newsworthy then.