قُلْ أَرَأَيْتَكُمْ إِنْ أَتَاكُمْ عَذَابُ اللّهِ بَغْتَةً

Say:"Tell me, if the punishment of Allah comes to you suddenly..."

means, while you are unaware -- or during the night -- striking you all of a sudden,
 
أَوْ جَهْرَةً

or openly

during the day, or publicly,
 
هَلْ يُهْلَكُ إِلاَّ الْقَوْمُ الظَّالِمُونَ
 
 

will any be destroyed except the wrongdoing people.

This torment only strikes those who commit injustice against themselves by associating others with Allah, while those who worship Allah alone without partners will be saved from it, and they will have no fear or sorrow.

In another Ayah, Allah said;

الَّذِينَ ءَامَنُواْ وَلَمْ يَلْبِسُواْ إِيمَـنَهُمْ بِظُلْمٍ

It is those who believe and confuse not their belief with Zulm, (wrong or Shirk). (6:82) 

Allah's statement