Symptoms. Symptoms of giardiasis are generally related to intestinal problems. You may experience diarrhea or excessive gas and flatulence. Feeling nauseous or having an upset stomach is also common. You may also feel pain and cramps in your stomach. Your stool may become greasy and you may start to lose some weight. Giardiasis often goes away by its own, but you may still experience the symptoms even after the parasites are gone. Generally, you can expect symptoms to last for up to six weeks. However, if you are experiencing symptoms such as bloating and nausea for longer than a week, go see a doctor to have your stool checked out. This is especially important if you have recently traveled to countries where parasites are more common.