A mental confusion when attempting to understand the anomaly which is the self. Quite common in adolescents, disillusioned religious converts, and the like. The root of the question

Who am I?

It's what happens to us when we pause what we're doing for a moment, and step outside of ourselves, and look at who we are.

It can be scary to see somebody different than you were expecting to see.

Or not see anybody at all.

An identity crisis can occur when we ground our identity in materialistic things or features, and discover that these fail to fully describe or capture the I. For example, beauty, appearance or style. It can also occur when we ground the individual in a belief system, and those beliefs change - for in the same way, these do not define a person, and when a person's beliefs change an identity crisis can occur. One is not merely a vegetarian or a conservatist.

Unfortunately, I don't yet know the antidote...

But it helps to remember that you are more than your beliefs, and that often an identity is indescribable.