Could have been Le Bonque and heat fatique, low/high blood sugar, take your pick. It's been very hot in my locale last week, 35C - cycling 20 miles in it was ok, but I was drinking a litre of water mixed 60% 40% with fruit juice with half a teaspoon of salt every hour. Much later, working moving bricks in the hot sunny yard I was hit with a headache and the shakes, sprayed myself, fully clothed, with cold water from the hose, got out of the sun and drank more fruit juice and water. OK after about 15 minutes.

I won't go anywhere on the bike without at least one bottle of fluid on it. Keep a couple of snack bars on the bike too. Scary if it happens away from the house.

Wear a hat.