I went riding my bike on an 80 degree day. When I arrived home, my heart was pounding really hard, I was sweating immensly, I felt tension in my neck, I felt faint when standing, and I saw bright colors creeping in from the sides, top and bottom of my eyes. This was reacurring for the next day and a half. I went the hospital thinking I was having a heart attack. They did blood tests, said there was nothing wrong with me and sent me home. After I arrived home, I walked the dog and when I bent over to pick up hlis droppings, I felt the problem again. I feel weak and distraught. Please help me.