Question

He was in terrible pain or at terrible pain? ​

Answer 1

He was in terrible pain.

Step-by-step explanation:

This is because, in this context, if you use "at" it would be referring to a particular place, instead of a feeling. It would not have been grammatically correct.

Hope this helps.

Answer 2

He was in terrible pain.

Step-by-step explanation:

'at' is usually used in case of places .

So,

He was in terrible pain, is grammatically correct.

Hope it helps!

Have a nice day:)