Can my mind be 'taken over'?

No, you will not lose the ability to monitor what is said to you or is happening, even if you cannot remember anything of the treatment your subconscious mind does.

A reasonable metaphor is to imagine that you have the solution to your problem(s) within your own mind (which, of course, you do) but is on the other side of a very dirty window. My job is to guide you towards cleaning away the grime so you can access that solution.