Be a bag/bundle of nerves
Definition 1 of 1
Pro Tip 1/3Intensity
The phrase suggests extreme nervousness, more than just being slightly worried or anxious. 
On my wedding day, I was such a bundle of nerves, I could barely say 'I do.'
Pro Tip 2/3Temporary State
This phrase usually refers to a temporary condition, often before an important event. 
The students were a bag of nerves just before the results were announced.
Pro Tip 3/3Colloquial Usage
It's commonly used in informal contexts, such as conversations between friends. 
I'm a bundle of nerves every time I have to drive in heavy traffic.