Generally, a side flopped bunny is pretty comfortable. Mine willlay all stretched out on their side, eyes half closed... Dead bunny flop? (Sometimes I'm convinced they are dead! And they look SO annoyed when I disturb them!)
And they will lay with their feet all stetched out behind them... making the Flemish almost a meter long! And they look quite comfy to me. I don't notice any distress.
A rabbit in discomfort, gas, stasis, pain of any kind, looks different. And if you know your rabbit, you will see it right away. Their eyes look different, they tend to hunch and sit all tucked up, they tend to shift their weight from side to side...They don't want to move, won't come when called, may not take a treat... you know something is wrong.
The only time I've seen a bunny stretched out in discomfort was from heat stroke. The rabbit was all stretched out with it's head thrown back at an unusual angle, and it was drooling and wet around the mouth. We saved it, but it took a lot of effort to get it's body temperature down and stablize it. But just looking at her, it was very obvious thatshe was in distress.