It's crazy what can happen in a day;
in an hour; in a moment; in the blink of an eye.

One minute you're fine, the next you're in utter chaos.  
One minute you're complete, the next you're empty.

All in a matter of seconds the sky can go from being bright and clear to being grey and disastrous and the same can be said about people.

You never know when a storm cloud is going to strike until it's too late and you're stuck in the rain without an umbrella.