Boxers over heating

Well I went to the dog park today just like every other day with Deuce.  It was around 70-75 degrees here in Kentucky and Deuce got a little sick.  After we were there for about an hour he started throwing up and doing a lot of dry heaving.  Lots of mucas and what was left of his food from this morning.  He looked jjust pitiful.  So I took him to get some water and her threw that back up.  Then I poured some water on him and it seemed to make him feel much better.  Has anyone else ever had this problem before or would it be from some other reason.  He and my roommates dog did chew up a plastic bag that some treats came in this morning as well.