how hard did you fall? was it on concrete? wood floor? carpet?
depending on all those, it can vary whether your skull can be deformed from that or not.
if you fell on carpet, no, it's probably not deformed. when you are 4 years old, your bones have already strengthened (so it's not soft like a baby's head). if you fell on concrete, it wouldn't be DEFORMED but you may have trouble areas regarding like math or practical thinking (depending again the angle at which you fell, etc.)
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