be scared witless
To be very severely frightened or worried. I was scared witless when I I heard footsteps on the staircase in the middle of the night. I'm scared witless that the tests are going to come back positive for leukemia.
be scared/bored ˈwitless
(informal) be extremely frightened or bored: Despite his reputation as a tough guy, he admits that he was ‘scared witless’ when he first arrived in New York.