Did i get heat exhaustion?

Today it was around the 80s and i was out doing colorguard outside when all of a sudden i became very dizzy and i couldn't see at all, it was like somebody was shinning a flashlight into my eyes. Well then i went to get water and i was fine after a few minutes. I guess it would that i haven't been out in the sun much. But i really don't want to be like this every time. What would you do to prevent this?