Me and my partner were playing with our 18 week old daughter earlier,and I made her jump,she then started to shake really badly and was making noises,at first she looked excited and like she was smiling at it it lasted quite a while but I am not sure if this is normal.I would appreciate your help,thank you.

Contact your pediatrician. This could be perfectly normal, however, we are not able to diagnose over the internet. Never trust the health of your child to strangers.

I agree, it could just be her anxious reaction, it could be something more serous. Either way, her pediatrician NEEDS to know.