There are several things that can make you feel everything tasting sweet. It can be caused by viral infections in the nose or back of the nose. Other causes are alteration to the sense of smell and inflammation in the mouth or gums.
1 Additional Answer
Perhaps you ate the miracle berry, the Synsepalum dulcificum. It is a very unique fruit in that it changes the way your taste buds react to sour flavors. For an hour or so after eating the berry, everything you eat will taste sweet! You can find more information at www.nytimes.com