First of all, it's not weird.
These experiences happen more often, however the way you describe it is somewhat different from what I think it is.
It seems to have the characteristics of a Kundalini experience, Kundalini - Wikipedia, the free encyclopedia
<-- link to Wikipedia , but from what I understand this feeling starts at the base of the spine, and not the stomach area, so this is making me doubt a bit.
Itlandm knows most about Kundalini, I am hoping he will pick this thread up.