Monitor her for the next 24 hours. Send her to KK A&E immediately if she appears excessively sleepy, listless, keeps crying unconsolably or throws up.
The good news is that most likely your baby is OK. It takes quite a big fall for anything major to happen.
My baby has bumped her head many times against the cot. It still happens especially when she flips in the middle of the night.
I understand your worry though. I was super worried when my baby fell off the bed (and I was right in front of her)!