Help!

Alyssa • Mom of 1 beautiful baby boy 👶🏻 7/8/19

My son is almost 6 weeks old and today my husband was holding him and he went to go move him to stand up from the couch and as he was still holding him my son fell backwards and was upside down for a few seconds. He didn’t hit anything but he was crying for a while after. He appears to be normal now as he is eating and moving all around but what are signs that something would be wrong???