Self-stimulated mental nervous sensation.

During my entire life I've been able to "feel" something within the center of my head/brain that I can stimulate somehow which creates a pleasurable sensation that travels from my head to the rest of my body in a wave.

Is this some sort of gland within my brain that I can stimulate at will or just some nerve?

I've never heard of anybody discuss this aspect of our physical makeup. If other people can do the same thing that is.

To keep this on topic, I also don't know whether or not this strange mental trick I can perform is healthy or not. So far I've never suffered any ill effects from it, just positive feelings, but you never know.

Pineal gland emitting serotonin...?