And when I am going to touch your forehead right now, just close your eyes and notice how a pleasant feeling of relaxation will spread (more and more) throughout your body.

I'd say.

I wouldn't use "going to" here. That would be if you are announcing what you are planning to do next: "Next, I am going to touch your forehead."

And when I touch your forehead in just a moment, close your eyes and experience how a pleasant feeling of relaxation spreads ...

or

And as I touch your forehead right now, ....

You can't use "going to" in the first case here, it's an adverbial clause of time, where future tenses of any kind are banned.

The second instance is certainly grammnatical, but you have to be a little careful. It suggests there is no possibility that this feeling will not happen. That is probably what is desired here, but be aware that "going to" is highly marked, i.e. not the default (which would be "will").

"inside you" is better.