Issues With Me. These type of thought.

I am facing a problem that whenever i went to my college to give exam during my exam i start getting negative thoughts like: "if i have vomiting issue here how will other reacts" i don't know why i have this type of thought and after thinking this i started feeling like nausea or like vomiting during the exam and only one thought in my mind continuously runs that what others will say if i have vomiting issue and this causes me to feel more like vomiting and it effects on my exam,my heart beat also increases and i start getting sweating also. Now due to pandemic i am giving Online exams but i am facing no issues but don't know what happens to me during offline exam in the exam hall with these type of thought.