I have fainted twice and cat scan was negative, lab results normal?

Hard to evaluate: There are a lot of causes that depend on your age or medical conditions. In younger women, fainting can be due to a low blood pressure from not having enough to drink, extreme heat, or alcohol, an eating disorder, or fluid loss from vomiting or diarrhea. A nervous system reaction from something upsetting can be the cause.Older people can faint due to some medications or heart problems.