Why are my goldfish sitting at the bottom of the tank?!?!?!???!?

I have two. They just recently had a weird poop. Im going on vacation for two weeks next week I don't want them to die!!! They are commet tails and i just cleaned the tank. I don't have enough time to buy any special stuff but someone help me. Also the water temperature is fine. I dont wanna add snails or anything but is this a digestion problem or something. Is there anything i can do. I don't know what the nitrate and ph level stuff is, but that stuff shouldnt be a problem because i use distilled water and they have gravel and decorations.