Filled with consternation (6)
(Other definitions for alarmed that I've seen before include "Frightened, frightened by danger" , "In a panic" , "Worried" , "Flapping" , "as a door handle may be?" .)
'filled with consternation' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for aghast that I've seen before include "What's carried in bag has teacher" , "Very unhappy" , "Amazed" , "Taken aback with horror" , "Filled with consternation or horror" .)