I didn't watch last night's game (fortunately) but I saw in the box score that Span was replaced by Mastroianni in the 8th inning.

 

This morning I checked the injury report list, and Span is on there day-to-day for dizziness.

 

Maybe I'm being paranoid, but is anybody else concerned about this, given his history of concussion symptons?

Yep, that should kill his trade value a lot.

I'm a little worried, but they said it was due to the heat. Probably just dehydration.

They probably should have said "dehydration" instead then. Bringing attention to the potential of a concussion-related issue tells me that he is not going to be traded.

They should had traded him while they were ahead...