Panicking in a stall or spin is kind of a normal human response to losing control over something that humans weren't built to be doing in the first place. There's really nothing abnormal about it, if you look at it that way.
The key to overcoming it, then, is a thorough knowledge of why these things happen, and a confidence resulting from much training and practice that you can, in fact, remain in control and recover from these situations. It's the feeling of loss of countrol that triggers the anxiety. Being confident in your ability to regain control will ameliorate it.
I suggest you hit the books and learn more about aerodynamics, especially the aerodynamics of stall, spins, and recovery; and also work with your CFI to thoroughly understand every stage of the process. Devote a few hours to nothing but that until you get so good at it that it gets boring.
By the way -- hiding this from your CFI is... well... let's just say unwise. Just don't use the word "anxiety," "panic attack," or anything else that sounds shrinky. "Nervous" will probably work. "CFI, stalls and spins get me nervous. I think I need to learn about and practice them more so I will be more confident."
-Rich