Legal Considerations
You must have a reasonable fear of harm to use physical force to defend yourself. If you inflict serious bodily harm or take another person's life, you must be legally justified. Only when you fear for your own life or that of another can you use lethal force. Under English common law, deadly force is never justifiable to protect property.
Reasonable force is best viewed on a sliding scale. The level of force employed is often dependent on an assailant's capability, opportunity, and the intent. You can measure an attacker's capability in several ways. A weapon, large physical size, or displayed martial prowess, such as a fighting stance, all increase the assailant's measure of capability. American law, for example, generally recognizes a "disparity of force" when an attacker possesses recognizable physical advantage or prowess, such as significant height, strength, weight, or trained fighting skills.
To assess the necessity of using force, you must look at several factors, including your opportunity to retreat. Retreat can be problematic if you are with another party such as a child, your wife, or an elderly person, or if you are in an enclosed area. Intent often involves the wielding of a weapon and verbal threats to your life and limb.
You should not have fear, you should have confidence in how well you were trained, and how you react.
In Krav Maga, every student must sign a declaration that they understand the law (as I stated above) as part of their contract...this isn't done where you learned martial arts?
Sued? If your life was threatened, or your loved ones, I wouldn't worry about being sued, I would be concerned about being alive tomorrow.
Talk with an advocate, lawyer, or your local police department.