Nirvana is a loaded word, but I have experienced a feeling I'd call the loss of ego. It was one of many gifts received from an erratic sleep schedule -- another was sleep paralysis, and yet another was hallucination. Meditation's physiological benefits can be enjoyed without religion, and even some concepts like "energy," I think can be utilized without taking them literally. As in the "energy" imagined in some visualization techniques -- think of it as a means of focusing and directing your attention, rather than some woo-woo force emanating from the earth or godhead.

Sam Harris made a pretty big deal about this in his speech at the conference.  Personally, I think his ideas were fairly reasonable, and he just found the worst possible way to say them to a bunch of dyed in the wool atheists.

As others have pointed out, there's nothing mystical about meditation.  There's also no guarantee that you'll find anything that will make you happy through meditation.  Daniel Dennett made a really good point when he noted that the vast majority of people who go into caves for three years to meditate don't say anything useful or interesting when they come back.

I'm a big fan of cognitive therapy.  I think you might want to give that a look.  It's not something you even need a therapist for if you're truly honest with yourself and aren't afraid to ask hard questions.  Just buy a textbook from a college bookstore and learn how to do it yourself.

Here's the basic overview:

* Humans develop "core ideas" that are more or less hard-wired into our brains when we are still quite young.

* These core ideas help us form shortcuts so that we don't have to reason through everything from the beginning.  They're like our own personal axioms -- things that are self-evidently true, and don't need to be evaluated further.

* The problem is that sometimes we form core ideas that are false.

* False core ideas lead to lots of false beliefs that we may not even consciously know we have.

* Identifying false core beliefs leads to identifying self destructive behavior patterns.

* Identifying self destructive behavior patterns leads to identifying "triggers" that cause us to engage in those patterns.

* Once we identify the triggers, we can begin to reprogram ourselves.  When a trigger happens, we consciously override it.  Over time, our new behavior patterns replace the original ones, so that we now have true core beliefs and healthy behavior patterns.

 In fact, I can't think of any reason why you couldn't meditate as a means to discovering false core beliefs.  Why not have the best of both worlds?  Anyway, check out cognitive therapy.  Nothing can guarantee happiness, but I've got a lot of personal and anecdotal evidence that it can work.