Hmm.. I'm glad you're practicing your interviews; have you tried practicing in front of the mirror? Body language and eye contact plays a big role with recruiters when you're trying to answer their questions. If your body language doesn't match your response, they have reason to doubt your confidence on your answer. If you're thinking of a response that's hard to answer, don't use "um" or "uhhh"... use silence and think about what words you'll use.
Also, make a list of your strengths and weaknesses. Be prepared to have an answer for your weaknesses.
With your strengths, make sure you sell it but don't be pompous about it; add a dash of humility and give examples on how you were an effective employee.
Use positive language when speaking to the interviewer and don't use passive words like "would". EG: Instead of, "I would be an excellent employee at your facility," say "I can add onto your facility a caring worker that thrives on team work and empathy to make the patient's stay memorable."
Lastly, don't and NEVER set yourself up for failure! That kind of mindset is self-sabotage. If you feel nervous before an interview, go to the bathroom and splash water on your face (if you are wearing make-up, run cold water on your hands), and TALK yourself in front of the mirror to compose yourself.
I play lots of sports and my coach used to say that even if you're playing with a team that you know is way better and stronger than you, you play the game you know how with your own style --- don't feed into your enemy's mind games but play the game to WIN.
I also learned this trick that works very well for me, when you feel scared, force yourself to smile and think of a happy thought (it's best to know what makes you happy beforehand). For some reason, looking at myself in the mirror while forcing myself to smile is a silly thing and gives me a chuckle to help me recompose myself.
I hope this helps on your interviews! Best of luck!