Jesus asked this question to help them see their lack of faith. This may be written as a statement. AT: "This is not a time to be upset and crying." (See: [[rc://en/ta/man/translate/figs-rquestion]])
Jesus uses the common word for sleep, and so should the translation. The reader should understand that the people who hear Jesus laugh at him because they truly do know the difference between a dead person and a sleeping person and they think he does not.