The indefinite article

[Mister Nutty]

Hi,

Is the indefinite article required in front of "fever"?

I fell seriously ill with a fever.

Also, is this formal or informal to say? I have to add this in a formal letter. What about "I was suffering from fever/ I was ill with fever/ I was fevering"?

Thanks,

Mr. Nutty

[Raymott]

Hi,

Is the indefinite article required in front of "fever"?

I fell seriously ill with a fever.

Also, is this formal or informal to say? I have to add this in a formal letter. What about "I was suffering from fever/ I was ill with fever/ I was fevering"?

Thanks,

Mr. Nutty

You'll get different regional responses. We say "a fever" in AusE.
You can say "I was feverish", but not "I was fevering".