HI, thanks for using healthcare magic The fluid loss from the diarrhea , decreased intake would likely cause mild dehydration. This can then cause the feeling of almost passing out. Nausea, diarrhea, headache, dizziness are most commonly related to an acute viral infection of the stomach and intestines. The main aspect of treatment is the use of enough fluids. The best fluids would be oral rehydration packets or a sport drink such as gatorade. Since he is nauseous , he should start out with small amounts at a time. Probiotics , either on their own or in yogurt, would also help. I hope this helps