First of all, it would be best not to try things you "heard about" on the internet from dubious sources. Laying a chicken on its back can cause aspiration of fluid that may be forced by this action to back up into the chicken's throat. You could end up with dead chicken when it chokes.
It sounds like your chicken could have a crop disorder if the crop is full of fluid, as opposed to a normal golf ball size clump of solid food. Watery poop can also be a symptom of a crop disorder as only fluids are making their way through the digestive system due to the crop not emptying properly.
However, it takes 12 to 24 hours to confirm some crop disorders. You need to check the crop in the morning before a chicken drinks or eats anything. If the crop is full in the morning, nothing is being digested, so the crop stays full. This can cause starvation over a period of time.
One crop disorder can be diagnosed immediately, and that would be impacted crop. It would feel over-full and hard and lumpy, and could have a rancid or sour smell due to it fermenting and growing bacteria.
A chicken with impacted crop and often a yeasty crop will often do neck swivels, sort of like a snake does when curled up and threatening a predator.
Here is more information.
https://www.backyardchickens.com/ar...w-to-know-which-one-youre-dealing-with.73607/
