If the fall is on the floor from his standing posture, it might not be a significant one. But if he has fallen from a table or bench, its worthy to have a word with a doctor.
Do you see any swelling in that area of his head? Does he cry on touching that area? Did you see any ear or nose bleeds? If yes, please see your doctor.
associated with head injuries is a forceful one and not associated with nausea
And yes vomiting can happen due to many other reasons as simple as overfeeding.
So observe him carefully. If he develops further episodes do not hesitate to contact a doctor.
Hope you find my answer helpful.