If a baby falls down by chance and starts crying that is the first positive sign. if the child goes still and quiet then it becomes a sign that there could be some injury to the head. The baby should not loose consciousness which means baby should be active and alert for a while after the fall. Vomiting is not a good sign. However since you mention spit up it could be a remote incidence. The next 24 hours should be observed for all above things has the reaction of a fall can happen even later. If concerned or if baby continues to spit up more than normal please visit the doctor.