If you say that you are bushed, you mean that you are extremely tired. I'm bushed. I'm going to bed. = beat. very tired (Probably from bushed 'lost in the bush ( BUSH2)' (19-20 centuries))
very tired; "was all in at the end of the day"; "so beat I could flop down and go to sleep anywhere"; "bushed after all that exercise"; "I'm dead after that long trip"