Also - to those who say you know your child...
You do, but you also don't.
The essential nature of all children is continuous change, and continuous intellectual development.
Mine were confident sleepers until they gained intellectual insight and imagination - things could exist in the dark...the all hell broke loose!
And, as others have said, the first indication of illness in a child is often whinny and weepy.
I hope both parents and child are ok, and I hope their travel was not urgent.