This depends on whether the attacker was armed or was just lunging at you unarmed. If unarmed, you may be considered to be using more force than necessary to repel the attack or to defend yourself. However, if the person was trying to kill or cause great bodily injury to you by choking you or banging your head against pavement, then you could assert that you had a reasonable belief that you were in imminent danger of death or great bodily harm and were justified in using deadly force.