I recently returned from Nepal. I was healthy the entire time that I was there, and was very careful about only drinking boiled water etc. I have been back for almost a week (six days) and in those six days have lost 4 to 5 pounds. I lost weight while in Nepal (6 pounds), but that made sense because I was trekking 8 to 9 hours a day while there. Since being back I have been having a hard time sleeping, have been having stomach pain after eating, have been light headed to the point of nearly passing out, and, as I said, have been losing weight despite eating the amount I ate before leaving for Nepal. I do not have diarrhea and have not been vomiting. I have been steadily losing weight for 9 months to a year, so I typically only eat 1,500 calories a day, but am working on stabilizing my weight by increasing intake. I am worried because my weight is low for my height (I amd 5'9 and 118 pounds) and because I feel very weak.