Are my rabbits play chasing, or are they fighting?

I've been bonding my rabbits for a little over a week now and theyve been going great. they love to groom and snuggle with each other. however sometimes (especially at night!) one of them will flatten their ears and run at the other and they'll start chasing each other. theres no t or biting, but their are tails raised and their ears are back. after a few seconds theyre fine again and start to cuddle more. is this fighting, or are they just playing?