short staff

Yesterday my coworker called out so that left me with all the work. When i spoke to my manager she said she had no one to send to me. I have 3 drs .working and 8 rooms to manage by myself. Later that day the house keeper came and told me that upstairs they have 3 ppl working and they only have 3 drs and 5 rooms. how is that fair i am only one person and doing the work that three people are doing upstairs. and you have no one to send to help me. by the end of the day my body was in physical pain. I want to ask my manager how is that fair? but I don't think that is the right way to approach the situation.