Spanish conjugation
Correct form of ser or estar in front of nerviosos
2 Answers
This is temporary state, that's why estar not ser.
Temporary and permanence have NOTHING to do with ser and estar. The reason it is estar is because it is a condition. Here is an example of a permanent state in which estar would be used:
He is dead. Él está muerto
Él es muerto would say that it is a defining characteristic of that person (which it's not). If someone were to ask you "What's he like?" Dead would not be a description you would give them.
Estar is used for states or conditions. Ser is used for characteristics (attributes, traits and qualities).
estoy Nervioso...
This is temporary state, that's why estar not ser.