Farting as you relax and when you bring your knees up towards your chest (common when you sleep on your side) is pretty normal. It might also be a timing thing based on when you go to bed relative to when you’ve eaten.

You might look into why you fart so much if it’s excessive. For instance, I have an odd food intolerance called fructose malabsorption - excess fructose doesn’t get digested, so it just ferments in my intestines. If I eat a lot of it, I’ll get massively painful diarrhea, but usually I just get some gas.

The same thing happens with people who are lactose intolerant: they can usually have some amount of lactose and they just get gassy, so some people don’t even realize they have it.

Other things can also cause unusual amounts of gas.