Toddler (13 mo) started crying non-stop, and we can't figure out what's wrong

Usually he is a fairly quiet young man, or if he cries, he will let us know what it is about.

Tonight, we we all asleep, and around 1030pm, he just started crying. Daiper was dry, and he has refused food, water, teethers, or even breast milk.

There are no marks or swelling anywhere on his body. He has now been crying for over an hour non-stop. Any advice, or ideas what to check would be helpful, dads. Thanks.

Edit: thank you all. He calmed down about 25 minutes after I wrote this. I appreciate all the suggestions. At the same time, the fear for his health means I'll be riding adrenaline insomnia for the next few hours.