Urgent! Goldfish laying sideways on bottom of the tank

[Reverie]

Last night my sister sent me a picture of my ryukin goldfish that is laying on the bottom of the tank barely moving. Today the goldfish is laying sideways and on the bottom of the tank. He did have swim bladder issues before that made him float but never sink. Unfortunately, I am in college and far from home so I am not able to test the water parameter. My sister lost the small tubes so she is unable to test it herself.
The goldfish lives with 3 other ryukin in a approx. 50g tank. Water is cleaned out daily and I've had them for over a year. Heater and filter is always on and the other goldfish with him are all healthy.

[Autumnsky]

Do more water changes might be helpful. Generally some positive response is found after water changing.

Water temp matching and dechlorinating.

Do you have Prime water conditioner there? It helps to neutralize the toxic things, ammonia, nitrite and nitrate. Dose as directed.

Maybe water changes were not done.

Or too much food was fed possible, causing unsafe water quality.

Or filter pads were changed /thrown out and you lost the beneficial bacteria?

I'm so sorry you are far away and can't address this directly.

Getting the water tested at a local fish store might be helpful. Find the tubes. A lfs might have extra tubes and be willing to give or sell them to your family member.

Knowing what you are dealing with is very important.

It's likely something was a cause. Water quality or bullying from another fish, or an illness.

Sometimes a stress in the tank can cause illness.