Looking down is a dead giveaway to lose tightness in your back. Don't do that.
Could be your set-up too, probably some flexibility/mobility issues at hand as well. But frankly I'd say it's probably that your upper back is just weak and that you should look to strengthening it with back exercises..
Cramps you pretty much just to fight through. Helps to make sure you get electrolytes and stuff, stay hydrated too.
One thing to look at is probably your technique as well. Little things can hurt that. For instance, if you start out of the hole and your hips move first it causes you to cave in. It shifts you forward ala a good morning, but it can also cause your upper back to cave.