That's mincing words. Being bipolar feels like an assault on my psyche that exists for no reason other than to make me miserable and to meticulously sabotage everything I do. I totally understand feeling like having a terrorist in your head, because it's a great way to describe how I feel sometimes.

In the title, the author is using a metaphor, which is a figure of speech in which a word or phrase is applied to an object or action to which it is not literally applicable.

And the contention here is that it's inappropriate (unless you mean to suggest that diseases are sentient or otherwise capable of intention to foment terror) and overplayed, and it ultimately corrodes the meaning of and devalues the word.