be scared silly

To be extremely shocked or frightened. She's been scared silly ever since that car almost hit her. I was scared silly going down into the dark cellar alone. We were scared silly when we woke up to the sound of the howler monkeys. We had no idea what it was coming from.

be scared stiff

To be utterly terrified; to be so scared that one cannot move. I was scared stiff when I heard someone in our kitchen in the middle of the night. Janet has been scared stiff after her encounter with that mountain lion. I was scared stiff when that car almost hit me. Luckily, my brother pulled me out of the way in time!

be scared to death

To be very severely frightened or worried. Hyperbolically alludes to having been frightened so badly as to have died from it. I was scared to death when I heard someone in our kitchen in the middle of the night. We were scared to death when we woke up to the sound of the howler monkeys. We had no idea what it was coming from. I'm scared to death that the tests are going to come back positive.

scared silly/stiff/to death, to be

To be extremely frightened; panicstricken. The earliest version of such hyperbolic expressions seems to have been to be scared or frightened out of one’s wits, which appeared in print in 1697: “Distracted and frighted out of his wits” (Bishop Simon Patrick, Commentary). Later it was frightened or scared out of one’s seven senses (used by Jonathan Swift and Sir Walter Scott), still later replaced by silly, with the same meaning. Stiff alludes to paralysis by fright, death to dying of terror. A mid-twentieth-century equivalent is to scare the pants off someone (Ogden Nash, and others). Also see shake in one's shoes.