Interview for assistant post

Wondering if anyone can give me some advice. I have an interview coming for a physio assistant post. I am a fully qualified physio but have been unable to secure a full time post, I just become extremely nervous during interviews and my mind goes blank when answering the clinical questions.

I had a physio assistant interview a few weeks ago but they said I was over qualified! I feel that an assistant post would suit me at the moment just to improve my confidence as it has been a while since I graduated. However I do not want the interview panel to think I am using this opportunity as "a foot in the door" for a future band 5 post. How would be the best way to go about this?

Any advice or if anyone knows the sort of questions they will ask would be a massive help!