There are many things which could have triggered this episode. Rabbits are prey animals and their senses are always tuned on “DANGER!”. Rabbits are creatures of habit and some may display anxiety when a situation suddenly changes. I always think of bunnies as a bit autistic: heightened senses, startled when faced with new situations and they may display panic when they’re overstimulated.
When your rabbit is thumping, please treat it seriously and try to comfort her. She’s really scared of something, even though you may not have picked up on it. Thumping is an action to keep the group safe, so as a group member it’s best to react to those thumps. I usually respond to his thumps by taking it as a serious warning, looking out the window for possible threats etc. When Breintje sees that I’m taking action it calms him down a lot. Usually it’s nothing more than something rustling in the garden, or some music far away.
You can actually spot different urgency levels: usually Breintje stands on his hind legs (periscoping), using his ears as a radar to pinpoint the oddity, and then gives a warning thump. One weekend night he was sitting next to me on the couch, and he was happily loafing. It was very late at night, and we like to spend these quiet hours next to eachother. Suddenly he flew up and started to give a series of very loud thumps. It really scared me because this was so different and sounded really urgent.
I grabbed my flashlight and started to inspect the gardens and the hallway leading to the bike storages. Then I quickly went into the house again to check if he was still so upset. I searched a bit further around the flat and I found out that the entire lock of the outdoors bike storage had been removed. Next morning a text to the neighbourhood whatsapp group showed that it must have happened that night. Breintje probably heard a burglary attempt, and it’s likely that my flashlight shining scared burglars away. So yes, sometimes a thump really is a danger warning, also to danger for humans.
Rabbits have very sensitive hearing and they have this instinct to communicate distress through thumping. It may be that she heard something which you can’t hear, but she found very distressing. The rumble of an engine, or vibrations from construction far away. One thing that also causes distress are shapes in the sky (which may be seen as birds of prey). Won’t be the first bun to get scared from an airplane, a kite or a plastic bag blowing in the wind. Rabbits have poor vision nearby, but like their wild cousins they can see pretty far to spot aerial danger. Another possible trigger is a new distressing scent, which may be simply because the rabbit isn’t used to it.
My bunny was super upset one morning, constantly thumping and shaking with fright. I had no idea what was going on and I had explored everything around the house already. Then I noticed that my neighbour across the hall had his front door open to get soe fresh air. He was playing music on a very respectable soft level, but it was dance music with a heavy bass. Breintje was constantly triggered by those vibrations. When the neighbour shut his front door, Breintje stood on his hind legs, looked around and promptly loafed.