What Causes Excessive Sweating,inflamed Face And Dizziness After Exposure To Sun?

Hi, I was just out in the sun in FL gardening, and became overheated, sweating, red face, and slightly light headed. I sat but when I tried to talk, my speech was garbled. After about 5 min., drinking water and deep breathing, I felt better. I had mitral valve repair on June 24 and am taking 100mg of amiodarone. I am 70 year old active female. One hour later, I feel myself again.
Thanks,
Dorothy