eternal, internal

Eternal or eternal means lasting or enduring forever, without a beginning or end--
Some religions teach a doctrine of eternal life.
Even the stars are not eternal, just very ancient.

Internal or internal means on the inside of something; contained within; physically or mentally--
The biology students are learning about internal organs.
You'll want to contact the internal affairs department.

Now that you know that, you can say--
"Talk of eternal life gives him an acute feeling of internal discomfort."

Note--"external" means on the outside of something--
"This product is for external use only; not to be taken internally."