Why be afraid of something that is entirely out of your control? If it happens, it happens, your fear will neither save you or prevent the situation, so just enjoy each day you awaken to as if it were your last.
Most ICSMs can be detected upon launch. And there are security measures in place to intercept the missles before they reach land. This is mostly why the United Nations likes to keep tabs on nuclear warheads and why secret warheads are frowned upon. Nuclear attack prevention has come a long way since the days of "dropping" a bomb on another country with a bullet-riddled prop plane.