I felt stomach, still cough, cough also very heavy, had a fever.

本人感到胃痛，还咳嗽，咳嗽也很重，有发烧。

youdao

I felt my stomach knot with apprehension.

我感到心里因为担心而揪紧。

《柯林斯英汉双解大词典》

I felt myself starting to get butterflies in the pit of my stomach; not out of nervousness, but out of the thrill of what I was about to do.

我开始感到不安，不是因为紧张，而是为自己接下来要做的事激动。

youdao

Having recently read your article about the business practices at Cintas Corporation, I felt sick to my stomach.

FORBES: Magazine Article

Even today, over six decades later, just hearing that long wail of the warning siren on old newsreels and films gives me that same cold knot of fear in the pit of my stomach which I always felt all those years ago.

BBC: Stanley Ross remembers the Blitz

Then I felt, across the lower part of my stomach, a first faint ripple of fear.

NEWYORKER: History of a Disturbance