No, passion should not just fizzle out of a relationship... lots of times it does, but it should not. Passion is what makes a relationship so exciting, and without it...hmmmm... I know for myself, I would definitely miss that.......and I'm not certain I would marry anyone if I didn't feel passion or chemistry for that person. They are emotions a marriage should NOT be without. I don't know whether to say that the relationship would be"unhealthy"without it..... it certainly would be boring and unexciting.... if you deem that"unhealthy", then that's your answer.