If you can't think of anything that would cause the flight response and saw it go fully down, then the issue may prove to be something that requires a vet, i.e. a blockage. If it came back up completely, it's wait a week then offer the next size DOWN food item from what they're on now. If he does it again, then you're going to absolutely need to schedule a vet visit to look into possible internal issues.
Also double-check your humidity and temps. Something may be amiss.