You're right-both sentences employ what is called inversion, for greater dramatic effect. In the first sentence "down"(a preposition) is put at the beginning of the sentence, which is often done in narratives. Other examples could be "Off you go!" or "We opened the box and out came a tiny animal."
The other sentence begins with a negative word (nor),which requires you to use inversion in the following clause.( Inversion basically means using the question word order). Other examples of the same process including negative words:
Not only was he talented but also really amiable. Compare: He was not only talented but also amiable.(-a neutral sentence,no inversion)
Never have I seen such a huge building. Compare: I have never seen such a huge ..
On no account can you touch this button. etc.
Inversion is typical of more formal ,often written English (or "dramatic narrative")
Other words which can be put at the beginning of the sentence with inverted word order include :Hardly/barely/scarcely or time expressions: hardly ever/rarely/seldom/not until etc.
Hope this is helpful!