i think there are lots of reasons a bun may act differently than usual.
first thing… is your bunny eating, drinking and pooping like normal? if bun has stopped any of these please go to your vet asap.
next i would check bun’s tummy to feel if it’s bloated. sometimes this can be an indication of stasis to come… in other words bun may still be eating & pooping but if there’s any tummy bloating they may need vet attention to prevent the bloated belly from causing bun to stop eating or pooping. if bun *is* bloated and has not stopped eating or pooping you can try to gently massage her tummy and give some simethicone drops (sold for gas relief in babies).
my buns tend to go through ‘moody’ days from time to time when they stay put in their enclosures so if there are no signs of illness this may be the case with your bun. i’ve found that other things like a new routine in their humans, new furniture, re-arranged furniture, new people or pet smells can also affect their mood.
lastly, how old is your bun? (sorry i forgot to check your bio first) is this a hormonal thing? if your bun is maturing and is pre-spay this can also affect her mood quite a bit.