Hi There are various reasons for dizziness and one of the common cause is heat stroke. As you said you went to fishing and was exposed high sunlight, it may be one of the possible cause To briefly tell you, heat stress occurs when the body cannot cool itself enough to maintain a healthy temperature. Heat-related illnesses include heat rash, heat cramps, dizziness or fainting, heat exhaustion, heat stroke, and a worsening of existing medical conditions. Overexertion in hot weather, sun or bushfire exposure, and exercising or working in hot, poorly ventilated or confined areas can increase your risk of heat stress Suggest -your self with thin clothing next time when you go out to fishing also try to be in the shade or can use portable land umbrellas -Hydrate yourself with fruit juices and plenty of water Also as you said Hypoglycemia may be one of the reason and if you are diabetic then it is a cause of concern otherwise nothing to worry Wish You Good Health Regards Dr Sridhar K