The symptoms of a stroke in a horse are: elevated respiration in an inactive horse (normal range is 4 to 16 breaths per minute).
Elevated pulse in an inactive horse, or pulse that does not drop after several minutes or climbs once exercise has stopped.
Profuse sweating or no sweating at all.
Elevated body temperature above 103F.
Irregular heart beat known as 'thumps'.
A depressed attitude.
Dehydration. Test for this by observing your horse's flanks. If they look caved in, he is probably dehydrated. Pick up a pinch of skin along your horse's neck. If the skin snaps back quickly the horse is sufficiently hydrated. If the pinched area collapses slowly the horse is dehydrated.
Applecart, I think you will find the most obvious sign of a stroke is collapse! The next obvious is going around in circles. I think you are describing heat exhaustion.
It appears you are right. Never trust Wiki Answers. I typed stroke in horses and that's what it gave me, never thought it could relate to heat stroke. Apologies for false info.