My bunny has never thumped but she has spooked for odd reasons before. You probably made a sound in the kitchen and she was just feeling jumpy. Our rabbit is quite strange this way, she doesn’t normally spook from sounds, other than the vacuum, but the other day, I picked up my guitar to play (which she always lies down and relaxes to) but instead, when I struck the first chord, she completely freaked out and went running under the couch. She also relaxes to the TV on a regular basis and nothing surprises her (we watch Die Hard, Castle, etc) but I watched an episode of Buffy the Vampire Slayer and the scene was meant to be startling to the viewer and it clearly worked because Willow even jumped and freaked out!
I always got worried the first few times this happened, now I’m pretty used to her doing this once in a while and just giggle at how ridiculous she is sometimes. Just go over and stroke your rabbit or bring her a treat to let her know everything is okay
That’s what I tend to do if she seems spooked for a prolonged period of time.