To compare it to gender dysphoria though, you’d have to be severely obese, or severely underweight, and believe you are the other one that you physically aren’t. If I weighed 400 lbs but believed I was actually a starving person that’s underweight, for example.

This… isn’t analogous. Being aware of and unhappy about the mismatch is specifically what makes it a dysphoria.

The questions were less about me getting your answer but more about pointing out how general the definition you gave was, and probing if your actual intended meaning was that vague. From looking at other comments, though, it looks like you did give someone else a more specific definition of what you meant:

I’m talking about the kind of uncomfortable that makes people consider surgery as the only alternative to suicide. I would consider that an illness.

Firstly, I’d like to point out that just HRT is both not surgery and sufficient for many trans individuals.

But, let’s say someone is extremely overweight, and they’ve been prevented from using regular methods (i.e. dieting and exercise), so their only option is surgery. If prevented from undergoing the surgery, don’t you think that depression and potentially even suicide are possible outcomes. Would this scenario, hypothetical though it may be, not also meet those requirements?

Now, let me tell you about Lipedema, a condition where large amounts of fat builds up on the legs. Regular diet and exercise methods can help with some symptoms, but cannot stop or reverse the condition. Liposuction (a fat-removal surgery), however, works—although it’s not a permanent fix yet and still can damage the body in the process. It fairly commonly can result in depression.

In a more general sense, “feeling uncomfortable in one’s own skin” is such a vague descriptor that it plausibly covers basically any nonlethal condition that can negatively affect an individual’s quality of life.