I think having some music on is a good idea, to give some background noise. I would also provide some extra hides if you can. If you try to stay calm that will also help. I would hang out with him but act as relaxed as possible with your body language, even if you are anxious too (even laying or sitting on the ground, watch a movie, etc).
Unfortunately if a bun “spooks”, the best thing you can do is leave them alone. Sometimes trying to catch and calm them stresses them out more, so just giving them space to calm down is all you can do.
Hanging a towel over fencing may help also. I had a bun that spooked once in his pen and would crash into the pen walls, so I think providing a visual barrier would have helped.
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The answers provided in this discussion are for general guideline purposes only. The information is not intended to diagnose or treat your pet. Seek the advice of your veterinarian or a qualified behaviorist.