Boyfriend said he had just washed the car. How to reply?

My boyfriend said that he had just washed the car, so he replied: After washing the car, you must remember to have a rest, or your back will be sore. The meaning of this sentence is to care about your boyfriend, which can promote the close relationship with your boyfriend and is conducive to the development of the relationship between couples. Because you must be tired after washing the car, you should say this sentence.