Is covert hypnosis easy to learn?

I was getting pretty frustrated the other day. I bought a course on this thing called conversation hypnosis — aka covert hypnosis — to help me with my sales career and it seemed to be going really well. My closing percentage was way up and it seemed like I was being more persuasive than ever. But then I got a lack of confidence all of a sudeen and it stopped working. Now I know it’s the not the fault of the course, but I need a way to regain my confidence so that I’m able to really implement what I’m learning. Any advice?