Difficulties with fermented foods

Hi, this is my first message on this forum. I've been eating nourishing traditions-type foods for several years. I keep trying to include the fermented products in my diet, because I know they are a valuable part of the diet, but I seem to have weird responses to them. For example, I just drank a small amount (about 1/4 cup) of beet kvass, and felt very tired about 15 min. later, and felt pressure build up in my ears. Sometimes, I've felt dizzy after fermented foods, and sometimes joint pain, or other disturbing stuff. Anyone had this problem or know what's going on? Does it mean I shouldn't eat them?