I hate to bring you back to ground. I hate to bring you back to reality. The reason your phrase is used is because it is quite general. There are many ways to rephrase it depending on what sort of 'bubble' they are in.

@Proshanto - 'she/ he is in illusions' doesn't make sense.

"i hate to give you bad news, but..."

burst someone's bubble= shatter someone's illusions about something or destroy their sense of well-being. so just tell him/her that she/ he is in illusions!