Most likely it is due to water quality or lack of oxygenation.
When you moved the tank, did you bring over the old filter media?
What im assuming has happened is all the bacteria has died during transport or before you set it up again, and thus your tank is now re-cycling. Which such a large bio load as it's stocked back to what it normally is, there will be large spikes in ammonia and later on nitrite and nitrate as the tank bacteria rebuilds itself up.
If you can, test your water for Ammonia, nitrite and nitrate. Ammonia causes fish to have a greater difficulty in utilizing oxygen and would explain the issue you are having.
Best advice for this i can give is frequent water changes. I'm talking 20% every 2 days for the next two weeks, then twice a week for the month after. After about 6 weeks from initial setup, the tank should be cycling well and you can reduce it to 20% once a week.
Another possible cause could be that your water has a very low oxygen supply, which can be fixed by either causing movement at the surface, via an air stone or power head, or planting some live plants.
Hope this helps out.
Goodluck
