About half of the emails I receive express concerns about strange, exhilarating or disturbing physical and mental experiences. I have great sympathy for these people, but I'm not trained to help in such matters, so all I can do is offer an opinion on where to look for more information.
In some cases the symptoms described seem to be related to kundalini, defined here as "the primordial Shakti, or cosmic energy, that lies dormant in a coiled form in the muladhara chakra at the base of the spine. Through the descent of grace (shaktipat), this extremely subtle force, also described as the supreme goddess, is awakened and begins to purify the entire being. As Kundalini travels upward through the central channel, She pierces the various chakras, finally reaching the sahasrara at the crown of the head."
For those of us who grew up in Western culture, this definition sounds like a fairy tale suitable mainly for psychiatric counseling. But with the rising interest in yogic practice and lore, Eastern concepts like chakra, subtle forces, and shaktipat are slowly being absorbed into popular culture. Western religious fundamentalists view these ideas as demonic, of course. But such folks assume that, except for the exceedingly tiny slice of reality that they inhabit, everything else is ultimately evil and/or demonic. Western science mostly ignores the idea of a kundalini energy because no one knows how to measure it, or even how to reliably confirm that it is what it is said (or more precisely, experienced) to be.
So when a writer asserts that he or she is otherwise normal, and has no history of mental illness, and they offer that they have been meditating for a few years, to me it suggests that they may be in the throes of a transformative experience that is better accommodated by Eastern traditions.
One website useful in exploring the concept of kundalini is by El Collie; especially helpful is her section on signs and symptoms.
Another good resource is an article by Judy Tart, offering sage advice for people having strange experiences, including those called psychic, mystical, or associated with a non-ordinary state of consciousness.