Webster’s 1913 has no entry under this spelling.
Shades of meaning
Fernald has no entry of its own for disquietude; he lists it under alarm, fear.
Where he writes about it:
Apprehension, disquietude, dread, misgiving, and solicitude are in anticipation of danger; consternation, dismay, and terror are overwhelming fear, generally in the actual presence of that which is terrible, though these words also may have an anticipative force. — from alarm