Consider this conversation:
— Iceland has more than 200 rainy days per year.
— Are you sure?
— No, I am not sure.
Is it valid or wrong English to say,
— No, sure I am not.
…in the last sentence?
I am German native speaker and in German both versions ("Nein, ich bin nicht sicher"/"Nein, sicher bin ich nicht") would be valid. The latter version is probably even preferred because that puts emphasis on the sure, as in "I do think that's how it is, but I don't know for a fact".
(It's impossible though to use the second version in an affirmation in German "Ja, sicher bin ich." This sounds like Yoda-speak, much like the English equivalent "Yes, sure I am.")
Edit.
If I would know the grammar of my own language better I could have asked: "Is (sentence) inversion allowed in English grammar?". The second German version above falls under the rule of (Sentence) Inversion and the English translations in the linked article and all answers to my question indicate that such an inversion is not allowed in the English language.
Best Answer
No, it is not valid (well, natural) English to say or to write:
It would be understood, but it doesn’t sound at all right. It would mark you as a non-native speaker.
The closest to what you are talking about would be the very archaic and/or poetic-sounding full inversion:
I suppose you could say that if you really wanted to, but it sounds completely affected. It really stands out. It’s not normal speech, although neither is it “illegal” as your first one nearly is. Maybe you could use something like this for the very rare and special occasion:
That doesn’t sound normal either, but it might be used to draw attention to the first word. Regular speech would simply be:
or sometimes,
Or if someone else had just said that they weren’t sure, then you could respond with and of:
Notice the inversion in the last one.
Notice also how unlike in German, you cannot in English use “too” or “also” in the negative: you must use “not . . . either”, or less commonly “neither” followed by subject–verb inversion (that is, verb–subject). This last point I mention because is a very common mistake that native speakers of German often make in English, and some possible answers to your question might lead you down the wrong path.