bump on head

My 7mths old LO had her first head bump yesterday evening. It happened on the lower bunk bed. Was sitting on my tummy then when I want to carry her lying flat on her back, suddenly she arch her back and her top part of her head hit the metal. She cried like a few seconds then stopped. Poor her, got a tiny bump on her head. Played with her, she smile. Drinking milk normal. No abnormalities. Is there anything I need to worry? What other things I should look out for? Should I be applying anything on her head? Haiz. I feel so bad.