I’m not a Christian, so it may be inappropriate for me to answer. But since Christian and Jewish ethics share the same fundamental ethical base, I am going to try.
Your life is worth the same as anyone else’s, which means it is of infinite value. If you are unjustifiably attacked and that attack puts your life in danger, you are justified and entitled to defend yourself with deadly force. That, however, never means trying to kill your attacker; your intent should be only to stop the attack. Once he is incapacitated or has otherwise stopped attacking you, you have an obligation to call for help and do what you can to save his life until medical personnel arrived.
Nor does being situationally aware mean becoming paranoid. more than 90% of the people whom you incidentally pass each day have no desire nor intent to harm you. Probably less than 5% are vicious killers. What you do need to do is to learn to quickly evaluate each person so that if one is behaving in a way which sets off your interior alarm, you are in a far better position to react to an attack if one should occur.
This may not be of any help at all to you; take it as you will.
