Learn Spanish (Latin America): A veces, uno siente que la fatiga es insoportable. - Sometimes, one feels that the fatigue is unbearable.

She can, but she doesn't have to. The pronoun uno is often used as a universal, gender-neutral way to say "one" or "generic you." However, it is very common and completely natural for a female speaker to use una (una siente) to include herself more personally in the generic statement.

How is "uno siente" different from using the impersonal "se siente"?

Both are used to make general statements, but uno siente is more personal. When a speaker uses uno, they are usually projecting their own personal experience onto people in general. The impersonal se (a veces, se siente que...) sounds much more detached, like an objective observation rather than a shared human experience.

Why do we use "es" (ser) with "insoportable"? Isn't fatigue a temporary state that requires "estar"?

While the feeling of being tired is temporary (e.g., estoy cansado), here we are describing the fatigue as a concept or an entity. By saying es insoportable, we are describing the inherent characteristic or nature of the fatigue itself. As a helpful rule of thumb, adjectives ending in -ble (like insoportable, increíble, posible) almost always describe intrinsic qualities and therefore pair with ser.

Is "fatiga" the standard word for tiredness in Latin America?