Why Would My 16 Year Old Son Get A Sharp

why would my 16 year old son get a sharp pain to left side/ upper back of head after a very loud sneeze? The pain is near the surface (pressure helps a bit), lasts over an hour with minimal relief, and left pupil noted to be somewhat smaller than right pupil. No other symptoms. This same pain occurred after hitting his left knee a few weeks ago, but the pain disappeared suddenly after an hour or so. Please reply to :
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