Actually Now that I think About it I’ve used the positive to counter the negative. I think it can actually help but it needs to be done with full recognition that you are working towards believing it and that the goal is to cancel out the negative talk, not to manifest anything.

I sure try to do something similar. Not just in my mind but also in real life. It's still a daily task for me though and it takes effort to be aware of the negative self talk going on quickly enough. Getting better and better at it though.

Less coffee, more rest ( sleep ) and more exercise make a difference.