When I've been in manic states I recall not only having feelings of intense love, euphoria and bliss, but also of having this incredible energy within me. I guess I was experiencing Viriya, the 3rd factor of the 7 factors of enlightenment. Sometimes I long to be manic. The typical long and deep depression which follows mania, I believe, is actually a mourning for its loss.

Here is what I've been able to scrap together about esoteric anatomy:
First, there are two higher centers in the human being, the spiritual heart and the spiritual crown.
Second, there is a hidden energy in the human being that 99.9% of us never encounter. In Buddhism, the term "viriya" refers to this energy, but we also find analogous terms in Christianity and Hinduism.
When we live the spiritual life, we learn about ourselves, simplify ourselves, withdraw from the world, and conquer our dysfunctions. What happens when we do these things is this energy emerges, and starts to rise up the spinal column. When that energy reaches the chest, the spiritual heart becomes activated and we undergo a profound transformation.
Later, if that energy reaches the crown of the head, it represents that someone has become a siddha or a perfected one.
Finally, from what I understand about the OOBE, in an OOBE that energy explodes out of the crown of the head while one is in the spiritual realm.
So, this energy rises in us in a linear way. If we have a sensation of it in the head, it means we have already unlocked the spiritual heart and so on. You would not have an experience of it without having been through the long journey of activating it and helping it emerge.
Some other points:
- A full body sensation is not viriya, but the sensation of the aura or spirit.
- Heat in the chest represents the activation of the spiritual heart.
- The stage of uncontrolled sobbing is connected with the activation of the spiritual heart.
- There are other centers than the heart and crown, in Yoga they list 7. However, we can simplify this into the most important two, the heart and the crown.
- The source of this energy appears to be the base or sexual center, so changing our relationship with sexuality is critical to getting on the spiritual path proper.