Hydration...If you have not noticed, it's hot.  Hydration is so very important when doing any activity outside and that does not exclude golf.  No, beer isn't the fix.  No problem with a beer after your round but it should not be the first thing you do.  Continuing to hydrate with water up to 45 minutes after your round is what you should be doing.  Then a beer at the 19th hole is ok.  Read this article on hydration and see how you measure up.  Click Here 

Don't ignore the warning signs.  Can't catch your breath, light headed, fatigue, not sweating, not urinating or if you do it is dark with odor.  All signs of not getting enough of the right fluids (Water,Gatorade or Powerade) into your system.  If you do overheat the fastest way to cool down is cold towels under the armpits and/or the crouch area.  This will aid in cooling you down.  The obvious thing is to get help quickly.  Call 911 and don't be embarrased.  It happens to a lot of people and is very dangerous.  I know, I had this happen to me in a matter of minutes.  I came off of a green and started to feel very fatigued.  By the time I got to the next tee, I could hardly get out of the cart to tee off.  I got to the fairway and could not stand up (8-10 minutes from the first sign).  They took me to the clubhouse and called 911.  I was down for nearly 1 hour.  I thought this could not happen to me.  I had never had this problem before.  Don't be a fool like I was.  Be smart and take care of yourself.