Feelings of grandiosity ("ego-mania") are a feature of a lot of different mental disorders. Some borderlines, some bipolars, and some schizophrenics experience feeling like they are invincible or wonderful and amazing, etc.

My schizophrenic boss had what are known as "delusions of grandeur" in which he believed he would save the world and had visions of himself with a long white beard and as a savior figure. This is a pretty extreme form, but it is one form that such a state can take.

Hope this helps!
Angela