Why Do I Feel Severely Lightheaded With Dry Mouth And Eyes?

Hi, I m 22 years old, my question is, the other day i feel like i don t know how to say this but maybe lightheaded and it s so bad my mouth feel dry my eyes feel dry too, i feel like dying my whole body feels dying, and when i go to the doctor and they do blood test and they said can t detect any problem with so I m totally confused.