I am not sure of the context to what you mean. Do you mean a thought was had and the internal reaction to it was very strong...as in the thought was taken as a threat to the system? And if s, was it a direct threat (X will happen to you) or indirect (the thought was so horrifying that it was internally defended against as though it was an outright attack)?
Or do you mean a thought was had within the system and this thought was communicated to an external person who then perceived it as an actual threat?